10 PRINT "A  PARANOID  PROGRAM  to  DIAGNOSE  FLOATING-POINT  ARITHMETIC"
20 PRINT "in  BASIC  v. A1.10  (May 1982) on the  IBM  Personal Computer."
30 '*****  Use only one of the following two statement lines !  *****
40   PRINT "          ... Single Precision version  ..."
50 ' DEFDBL A-H, O-Z : PRINT "          ... Double Precision version  ..."
60 '*****************************************************************
70 DEFINT I-N : I0=20 : ' ...  I0 = #( random trials of X*Y=Y*X , etc.)
80 GOTO 160
90 ' This program runs interactively putting all output to a screen.  The next
100 ' Subprogram pauses, allowing you to read the screen or copy it.
110 PRINT CHR$(7) : INPUT; "To continue diagnosis, press ENTER  [<-']  key:",X$
120 CLS : ' ... or  HOME,  or  ? CHR$(12),  or   FOR I=1 TO 22 : PRINT : NEXT I
130 K=K+1 : PRINT "Diagnosis resumes after milestone  #L =";L;",            ... page";K
140 L=L+1 : PRINT : RETURN
150 ' -----------------------------------------------
160 K=0 : L=0 : ' ... K = #( page of diagnosis ),  L = Milestone in program
170 PRINT : PRINT "Lest this program stop prematurely, i.e. before displaying"
180 PRINT "                 `   End of Test   ' ,"
190 PRINT "try to persuade the computer NOT to terminate execution whenever an"
200 PRINT "`error'  like Over/Underflow or Division by Zero occurs, but rather"
210 PRINT "to persevere with a surrogate value after, perhaps, displaying some"
220 PRINT "warning.   If persuasion avails naught,  don't despair but run this"
230 PRINT "program anyway to see how many milestones (#L) it passes, and then"
240 PRINT "amend it to make further progress.  (See program lines #250 - 370.)"
250 '________ Only for  Compiled BASIC  on the  IBM PC  ________
260 V8=0 : Q8=0 : ON ERROR GOTO 270 : GOTO 380
270 IF NOT ( ERR=5 OR ERR=6 OR ERR=11) THEN ON ERROR GOTO 0
280 IF NOT (ERR=5) THEN 320
290 IF NOT (ERL=3030 AND I=1) THEN ON ERROR GOTO 0
300 Y=-O : J1=J1+1 : PRINT S$;"BUG:  If X=0 then  SQR(-X)  stops the machine !
310 RESUME NEXT
320 E8=O2^63 : E8=E8*O2*F9*E8 : IF (ERR=6) THEN 340
330 Q8=O1+Q8 : Q9=E8 : B8=Q8 : PRINT "DIVISION by ZERO ..." : GOTO 350
340 V8=O1+V8 : V9=E8 : B8=V8 : PRINT "OVERFLOW ..." : IF (ERL=5530 OR ERL=5520) THEN V9=-V9
350 IF (B8>O1) THEN RESUME NEXT
360 J2=J2+1 : PRINT "were it not simulated here, it would Stop the machine!  This is a DEFECT." : RESUME NEXT
370 '~~~~~~~~           end of error-handler            ~~~~~~~~~
380 PRINT
390 PRINT "Users are invited to help debug and augment this program so it will"
400 PRINT "cope with unanticipated and newly uncovered arithmetic pathologies."
410 PRINT "Please send suggestions and interesting results to the author:"
420 PRINT "*(C) 1983                     Prof. W. M. Kahan,   567 Evans Hall,"
430 PRINT "  Apr. 19                     Elect. Eng. & Computer Science Dept.,"
440 PRINT "  ~~~~~~~                     University of California,"
450 PRINT "                              Berkeley,   Calif. 94720"
460 PRINT "*  You may copy this program freely if you acknowledge its source."
470 GOSUB 110 : ' ---- PAUSE ----
480 PRINT "Running this program should reveal these characteristics:"
490 PRINT "  B = Radix ( 1, 2, 4, 8, 10, 16, 100, 256, or ... ) ."
500 PRINT "  P = Precision, the number of significant  B-digits carried."
510 PRINT "  U2 = B/B^P = One Ulp (Unit in the Last Place) of 1.000xxx... ."
520 PRINT "  U1 = 1/B^P = One Ulp of numbers a little less than 1.0 ."
530 PRINT "  G1, G2, G3  tell whether adequate Guard Digits are carried;"
540 PRINT "   1 = YES ,  0 = NO ;   G1 for MULT.,  G2 for DIV.,  G3 for SUBT."
550 PRINT "  R1, R2, R3, R4  tell whether arithmetic is rounded or chopped;"
560 PRINT "   0 = chopped,  1 = correctly rounded,  -1 = some other rounding;"
570 PRINT "   R1 for MULT.,   R2 for DIV.,   R3 for ADD/SUBT.,   R4 for SQRT."
580 PRINT "  S=1 when a sticky bit is used correctly in rounding; else S=0."
590 PRINT "  U0 = an underflow threshold."
600 PRINT "  E0 and Z0  tell whether underflow is abrupt, gradual or fuzzy."
610 PRINT "  V = an overflow threshold, roughly."
620 PRINT "  V0   tells, roughly, whether  Infinity  is represented."
630 PRINT "  Comparisons are checked for consistency with subtraction"
640 PRINT "                      and for contamination by pseudo-zeros."
650 PRINT "  SQRT is tested.  So is  Y^X  for (mostly) integers  X ."
660 PRINT "  Extra-precise subexpressions are revealed but NOT YET tested."
670 PRINT "  Decimal-Binary conversion is NOT YET tested for accuracy."
680 GOSUB 110 : ' ---- PAUSE ----
690 PRINT "The program attempts to discriminate among"
700 PRINT "  FLAWs, like lack of a sticky bit,                          (J3)"
710 PRINT "  Serious DEFECTs, like lack of a guard digit, and       (J1, J2)"
720 PRINT "  FAILUREs, like  2+2 = 5 .                                  (J0)"
730 PRINT "Failures may confound subsequent diagnoses."
740 PRINT "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
750 PRINT
760 PRINT "The diagnostic capabilities of this program go beyond an earlier"
770 PRINT "program called  `MACHAR' , which can be found at the end of the"
780 PRINT "book  `Software Manual for the Elementary Functions'  (1980)  by"
790 PRINT "W. J. Cody and W. Waite.  Although both programs try to discover"
800 PRINT "the radix (B), precision (P) and range (over/underflow thresholds)"
810 PRINT "of the arithmetic, this program tries to cope with a wider variety"
820 PRINT "of pathologies, and to say how well the arithmetic is implemented."
830 PRINT
840 PRINT "The program is based upon a conventional radix representation for"
850 PRINT "floating-point numbers, but also allows for logarithmic encoding"
860 PRINT "(B=1)  as used by certain early WANG machines."
870 PRINT
880 L=7 : GOSUB 110 : ' ---- PAUSE ---- =====================================
890 J0=0 : O=0 : O1=1 : PRINT "Program is now RUNNING tests on small integers:"
900 F$="FAILURE:" : V$=" Violation of " : M$="  Multiplication"
910 O2=O1+O1 : IF (O+O=O AND O1-O1=O AND O1>O AND O2=2) THEN 930
920 J0=1 : PRINT F$;V$;"  0+0=0  or 1-1=0 or 1 > 0  or  1+1 = 2 "
930 Z=-O : IF (Z=O) THEN 960
940 J0=J0+1 : PRINT F$;" Comparison alleges that Minus Zero, obtained by setting" : PRINT "         X = 0  and then  Z = -X ,  is nonzero!
950 U2=.001 : Z$="Z" : B=1 : GOSUB 4640
960 O3=O2+O1 : O4=O3+O1 : IF (O4+O2*(-O2) = O AND (O4-O3)-O1 = O) THEN 980
970 J0=J0+1 : PRINT F$;V$;"  3+1 = 2*2 "
980 F1=-O1 : IF (F1+O1=O AND O1+F1=O AND F1+ABS(F1)=O AND F1+F1*F1=O) THEN 1000
990 J0=J0+1 : PRINT F$;V$;"  -1 + 1 = 0 "
1000 F2=O1/O2 : IF (F2+F1+F2=O) THEN 1020
1010 J0=J0+1 : PRINT F$;V$;"  1/2 - 1 + 1/2 = 0"
1020 L=10 : 'Miscellaneous variables: ========================================
1030 J0=J0 : J1=0 : J2=0 : J3=0 : ' ... count FAILUREs, serious DEFECTS, FLAWS
1040 G1=O1 : G2=O1 : G3=O1 : '  ... to record guard digits
1050 A$="  Add/Subtract" : B$="correctly rounded." : C$="chopped"
1060 D$="  Division" : S$="SERIOUS " : L$=" lacks a Guard Digit, "
1070 E$=" appears to be " : H$=" is neither " : Q$="Square Root"
1080 I$="  gets too many last digits wrong."
1090 P$=" test is inconsistent;  PLEASE  NOTIFY  THE  AUTHOR !"
1100 O9=O3*O3 : T7=O9*O3 : O8=O4+O4 : T2=O4*O8 : IF (T2-T7-O4-O1=O) THEN 1120
1110 J0=J0+1 : PRINT F$;V$;"  32 - 27 - 4 - 1 = 0"
1120 O5=O4+O1 : S=O4*O5 : T=O3*O4 : T8=S*T : ' ... T8=240
1130 X=T8/O3 : Y=T8/O4 : Z=T8/O5 : X=X-O4*S : Y=Y-O5*T : Z=Z-O4*T : IF ( X=O AND Y=O AND Z=O ) THEN 1150
1140 J0=J0+1 : PRINT F$;V$;" 240/3 = 80  or  240/4 = 60  or  240/5 = 48."
1150 IF (J0=0) THEN PRINT " -1, 0, 1/2 , 1, 2, 3, 4, 5, 9, 27, 32 & 240 are O.K." : PRINT
1160 PRINT "Searching for radix  B  and precision  P ; ";
1170 W=O1
1180 W=W+W : Y=W+O1 : Z=Y-W : Y=Z-O1 : IF (F1+ABS(Y)<O) THEN 1180
1190 '... now  W  is just big enough that  |((W+1)-W)-1| >= 1 ...
1200 P=O :  Y=O1
1210 B=W+Y : Y=Y+Y : B=B-W : IF (B=O) THEN 1210
1220 IF (B<O2) THEN B=O1
1230 PRINT " Radix  B = "; B : IF (B=O1) THEN 1270  :' ... else  B >= 2 ...
1240 W=O1
1250 P=P+O1 : W=W*B : Y=W+O1 : Z=Y-W : IF (Z=O1) THEN 1250
1260 ' ... now  W = B^P  is barely too big to satisfy  (W+1)-W = 1  ...
1270 U1=O1/W : U2=B*U1 : PRINT "Closest relative separation found is  U1 ="; U1
1280 PRINT : PRINT "Recalculating radix and precision ";
1290 E0=B : E1=U1 : E9=U2 : E3=P :'  ...  save old values
1300 X=O4/O3 : F3=X-O1 : F6=F2-F3 : X=F6+F6 : X=ABS(X-F3) : IF (X<U2) THEN X=U2
1310 '  ... now  x = (unknown no.) ulps of  1 + ...
1320 U2=X : Y=F2*U2+T2*U2*U2 : Y=O1+Y : X=Y-O1 : IF (U2>X AND X>O) THEN 1320
1330 '  ... now  u2 = 1 ulp of  1 + ...
1340 X=O2/O3 : F6=X-F2 : F3=F6+F6 : X=F3-F2 : X=ABS(X+F6) : IF (X<U1) THEN X=U1
1350 '  ... now  x = (unknown no.) ulps of  1 - ...
1360 U1=X : Y=F2*U1+T2*U1*U1 : Y=F2-Y : X=F2+Y : Y=F2-X : X=F2+Y : IF (U1>X AND X>O) THEN 1360
1370 '  ... now  u1 = 1 ulp of  1 - ...
1380 IF (U1=E1) THEN PRINT " confirms closest relative separation  U1 ."
1390 IF (U1><E1) THEN PRINT " gets better closest relative separation  U1 = "; U1
1400 W=O1/U1 : F9=(F2-U1)+F2 : ' ... = 1 - U1 = nextafter(1.0, 0)
1410 B=INT(.01 + U2/U1) : IF (B=E0) THEN PRINT "Radix  B  confirmed."
1420 IF (B><E0) THEN PRINT "MYSTERY: recalculated radix  B = "; B
1430 IF (B=O2 OR B-O9=O1 OR B=O1) THEN 1470
1440 IF (B>O8+O8) THEN 1460
1450 J3=J3+1 : PRINT "FLAW: Radix  B =";B;" is not so good as  2  or  10." : GOTO 1470
1460 J2=J2+1 : PRINT "DEFECT: Radix  B =";B;" is so big that roundoff propagates capriciously."
1470 L=20 : ' Test for fuzzy comparison ... ==================================
1480 IF (F9-F2<F2) THEN 1510
1490 J0=J0+1
1500 PRINT F$;"  (1-U1)-1/2 < 1/2  is FALSE, so this program may malfunction."
1510 X=F9 : I=1
1520 Y=X-F2 : Z=Y-F2 : IF (X><O1 OR Z=O) THEN 1540
1530 J0=J0+1 : PRINT F$;"  Comparison is fuzzy; it alleges  X = 1  although" : PRINT "          subtraction yields  (X - 1/2) - 1/2 = ";Z
1540 IF (I=0) THEN 1560
1550 X=O1+U2 : I=0 : GOTO 1520
1560 L=25 : ' End of test for fuzzy comparison.===============================
1570 B9=B-O1 : B9=(B9-U2)+O1 : IF (B=O1) THEN 1610 : ' ... B9 = nextafter(B, 0)
1580 X=-T8*LOG(U1)/LOG(B) : Y=INT(F2+X) : IF ( ABS(X-Y)*O4<O1 ) THEN X=Y
1590 P=X/T8 : Y=INT(F2+P) : IF ( ABS(P-Y)*T8<F2 ) THEN P=Y : ' Purify integers.
1600 IF (P=INT(P)) THEN 1640
1610 PRINT "Precision cannot be characterized by an integer number of sig. digits;" : IF (B>O1) THEN 1630
1620 PRINT "logarithmic encoding (B=1) has precision characterized solely by  U1 ." : GOTO 1650
1630 PRINT "but, by itself, this is a minor flaw."
1640 PRINT "The number of significant digits of radix  B  is  P = "; P
1650 IF (U2*O9*O9*T8<O1) THEN 1670
1660 J1=J1+1 : PRINT S$;"DEFECT: Precision worse than  5 sig. dec. is usually inadequate." : GOTO 1680
1670 PRINT
1680 L=30 : 'Test for extra-precise subexpressions:  ========================
1690 X=ABS( ((O4/O3-O1)-O1/O4)*O3 - O1/O4 )
1700 Z2=X : X=(O1+(F2*Z2+T2*Z2*Z2))-O1 : IF (Z2>X AND X>O) THEN 1700
1710 Y=ABS( (O3/O4-O2/O3)*O3 - O1/O4 ) : Z=Y : X=Y
1720 Z1=Z : Z=(O1/O2 - ((O1/O2-(F2*Z1+T2*Z1*Z1))+O1/O2)) + O1/O2 : IF (Z1>Z AND Z>O) THEN 1720
1730 Y1=Y : Y=(F2 - ((F2-(F2*Y1+T2*Y1*Y1))+F2)) + F2 : IF (Y1>Y AND Y>O) THEN 1730
1740 X1=X : X=((F2*X1+T2*X1*X1)-F9)+F9 : IF (X1>X AND X>O) THEN 1730
1750 IF (X1=Y1 AND X1=Z1) THEN 1780
1760 J1=J1+1 : PRINT S$;"DEFECT: Disagreements among the values  X1, Y1, Z1  resp." : PRINT X1;",     ";Y1;",     ";Z1 : PRINT "are symptoms of inconsistencies introduced by extra-precise evaluation of"
1770 PRINT "allegedly  `optimized'  arithmetic subexpressions.  Possibly some part of this" : PRINT P$ : IF (X1=U1 OR Y1=U1 OR Z1=U1) THEN 1850
1780 IF (Z1=U1 AND Z2=U2) THEN 1870
1790 IF (Z1<U1 AND Z2<U2) THEN 1810
1800 J0=J0+1 : PRINT F$;"Precision";P$ : PRINT "U1 =";U1;",  Z1-U1 =";Z1-U1 : PRINT "U2 =";U2;",  Z2-U2 =";Z2-U2 : GOTO 1860
1810 IF (Z1>O AND Z2>O) THEN 1830
1820 PRINT "Because of an unusual radix  B =";B;",  or exact rational arithmetic," : PRINT "a result  Z1 =";Z1;"  or  Z2 =";Z2;"  of an extra-precision" : PRINT P$ : IF (Z1=Z2) THEN 1850
1830 X=Z1/U1 : Y=Z2/U2 : IF (Y>X) THEN X=Y
1840 Q=-LOG(X) : PRINT "Some subexpressions appear to be calculated extra-precicely with" : PRINT "about   ";Q/LOG(B);" extra B-digits, i. e." : PRINT "roughly ";Q/LOG(10);" extra significant decimals."
1850 PRINT "  That feature is not tested further by this program."
1860 GOSUB 110 : ' ---- PAUSE ----
1870 L=35 : ' ================================================================
1880 IF (B<O2) THEN 1920
1890 X=W/(B*B) : Y=X+O1 : Z=Y-X : T=Z+U2 : X=T-Z : IF (X=U2) THEN 1910
1900 J0=J0+1 : PRINT F$;" Subtraction is not normalized, so  X=Y  does not imply  X+Z=Y+Z !" : GOTO 1920
1910 PRINT "Subtraction appears to be normalized, as it should."
1920 PRINT
1930 PRINT "Checking for guard digit in Multiply (G1), Divide (G2) and Subtract (G3) :"
1940 Y=F9*O1 : Z=O1*F9 : X=F9-F2 : Y=(Y-F2)-X : Z=(Z-F2)-X : X=O1+U2 : T=X*B
1950 R=B*X : X=T-B : X=X-B*U2 : T=R-B : T=T-B*U2 : X=X*(B-O1) : T=T*(B-O1) : IF (X=O AND Y=O AND Z=O AND T=O) THEN 1980
1960 J1=J1+1
1970 G1=O : PRINT S$;"DEFECT:";M$;L$;"violating  1*X = X ."
1980 Z=B*U2 : X=O1+Z : Y=ABS((X+Z)-X*X)-U2 : X=O1-U2 : Z=ABS((X-U2)-X*X)-U1 : IF (Y<=O AND Z<=O) THEN 2000
1990 J0=J0+1 : PRINT F$;M$;I$
2000 Y=O1-U2 : X=O1+U2 : Z=O1/Y : Y=Z-X : X=O1/O3 : Z=O3/O9 : X=X-Z : T=O9/T7
2010 Z=Z-T : IF (X=O AND Y=O AND Z=O) THEN 2040
2020 J2=J2+1
2030 G2=O : PRINT "DEFECT:";D$;L$;"so error can exceed 1 ulp" : PRINT "or  1/3  and  3/9  and  9/27  may disagree."
2040 Y=F9/O1 : X=F9-F2 : Y=(Y-F2)-X : X=O1+U2 : T=X/O1 : X=T-X : IF (X=O AND Y=O) THEN 2070
2050 J1=J1+1 : J2=J2-1+G2
2060 G2=O : PRINT S$;"DEFECT:";D$;L$;"violating  X/1 = X ."
2070 X=O1/(O1+U2) : Y=X-F2-F2 : IF (Y<O) THEN 2100
2080 J1=J1+1
2090 PRINT "VERY SERIOUS DEFECT:  Computed value of  1/1.00...001  is not less than  1 ."
2100 X=O1-U2 : Y=O1+B*U2 : Z=X*B : T=Y*B : R=Z/B : S=T/B : X=R-X : Y=S-Y : IF (X=O AND Y=O) THEN 2130
2110 J0=J0+1
2120 PRINT F$;M$;"  and/or";D$;I$
2130 Y=O1-U1 : X=O1-F9 : Y=O1-Y : T=B-U2 : Z=B-B9 : T=B-T
2140 IF (X=U1 AND Y=U1 AND Z=U2 AND T=U2) THEN 2230
2150 J1=J1+1
2160 G3=O : PRINT S$;"DEFECT: Subtraction";L$;"so cancellation is obscured."
2170 IF (F9=O1 OR F9-O1<O) THEN 2240
2180 J1=J1+1
2190 PRINT "VERY SERIOUS DEFECT: comparison alleges  (1-U1) < 1  although"
2200 PRINT "         subtraction yields  (1-U1) - 1 = 0  , thereby vitiating"
2210 PRINT "         such precautions against division by zero as"
2220 PRINT "         ...  if (X=1.0) then ..... else .../(X-1.0)..."
2230 IF(G1*G2*G3=O1) THEN PRINT "  These operations appear to have guard digits, as they should."
2240 L=40 : GOSUB 110 : ' ---- PAUSE ---- ====================================
2250 PRINT "Checking for rounding in Multiply (R1), Divide (R2) and Add/Subtract (R3):"
2260 R1=F1 : R2=F1 : R3=F1 : B2=B/O2 : T5=O1+F2 : ' ...  B2 = B/2 ,  T5 = 1.5
2270 A1=O2 : ' Is  B  a power of  2  or  10 ?
2280 A=B
2290 X=A : A=A/A1 : IF (INT(A)=A) THEN 2290
2300 IF (X=O1) THEN 2340 : ' ...  B  is a power of  A1 ;  if B=1 then  A1=2.
2310 IF (A1>O3) THEN 2330
2320 A1 = O9+O1 : GOTO 2280 : ' Is  B  a power of  10 ?
2330 A1 = B : ' ... unless  B  is a power of  A1  and  A1 = 2 or 10 .
2340 A=O1/A1 : X=A1 : Y=A
2350 Z=X*Y-F2 : IF (Z=F2) THEN 2370
2360 J0=J0+1 : PRINT F$;"  1/";X;" = ";Y;", and  ";X;"*(1/";X;") differs from  1."
2370 IF (X=B) THEN 2390
2380 X=B : Y=O1/X : GOTO 2350
2390 Y2=O1+U2 : Y1=O1-U2 : X=T5-U2 : Y=T5+U2 : Z=(X-U2)*Y2 : T=Y*Y1 : Z=Z-X : T=T-X : X=X*Y2 : Y=(Y+U2)*Y1 : X=X-T5 : Y=Y-T5 : IF NOT ( X=O AND Y=O AND Z=O AND T<=O ) THEN 2460
2400 X=(T5+U2)*Y2 : Y=T5-U2-U2 : Z=T5+U2+U2 : T=(T5-U2)*Y1 : X=X-(Z+U2) : S=Y*Y1 : S1=Z*Y2 : T=T-Y : Y=(U2-Y)+S : Z=S1-(Z+U2+U2) : S=(Y2+U2)*Y1 : Y1=Y2*Y1 : S=S-Y2 : Y1=Y1-F2
2410 IF ( X=O AND Y=O AND Z=O AND T=O AND S=O AND Y1=F2 ) THEN R1=O1
2420 IF ( X+U2=O AND Y<O AND Z+U2=O AND T<O AND S+U2=O AND Y1<F2 ) THEN R1=O
2430 IF (R1=O) THEN PRINT "  R1=0:";M$;E$;C$;"."
2440 IF (R1=O1) THEN PRINT "  R1=1:";M$;E$;B$
2450 IF (R1-G1=O1) THEN PRINT F$;M$;P$
2460 IF (R1=F1) THEN PRINT M$;H$;C$;" nor ";B$
2470 L=45 : ' ================================================================
2480 Y2=O1+U2 :Y1=O1-U2 : Z=T5+U2+U2 : X=Z/Y2 : T=T5-U2-U2 : Y=(T-U2)/Y1 : Z=(Z+U2)/Y2 : X=X-T5 : Y=Y-T : T=T/Y1 : Z=Z-(T5+U2) : T=(U2-T5)+T : IF ( X>O OR Y>O OR Z>O OR T>O ) THEN 2540
2490 X=T5/Y2 : Y=T5-U2 : Z=T5+U2 : X=X-Y : T=T5/Y1 : Y=Y/Y1 : T=T-(Z+U2) : Y=Y-Z : Z=Z/Y2 : Y1=(Y2+U2)/Y2 : Z=Z-T5 : Y2=Y1-Y2 : Y1=(F9-U1)/F9 : IF ( X=O AND Y=O AND Z=O AND T=O AND Y2=O AND Y1-F2=F9-F2 ) THEN R2=O1
2500 IF ( X<O AND Y<O AND Z<O AND T<O AND Y2<O AND Y1-F2<F9-F2 ) THEN R2=O
2510 IF (R2=O) THEN PRINT "  R2=0:";D$;E$;C$;"."
2520 IF (R2=O1) THEN PRINT "  R2=1:";D$;E$;B$
2530 IF (R2-G2=O1) THEN PRINT F$;D$;P$
2540 IF (R2=F1) THEN PRINT D$;H$;C$;" nor ";B$
2550 B1=O1/B : IF (B1*B-F2=F2) THEN 2580
2560 J0=J0+1
2570 PRINT F$;"  B*(1/B)  differs from  1."
2580 L=50 : '=================================================================
2590 IF ( (F9+U1)-F2 = F2  AND  (B9+U2)-O1 = B-O1 ) THEN 2610
2600 J0=J0+1 : PRINT F$;" Incomplete carry-propagation in Addition."
2610 X=O1-U1*U1 : Y=O1+U2*(O1-U2) : Z=F9-F2 : X=(X-F2)-Z : Y=Y-O1
2620 IF (X><O OR Y><O) THEN 2640
2630 R3=O : PRINT "  R3=0:";A$;E$;C$;"."
2640 IF (G3=O) THEN 2710
2650 X=(F2+U2)*U2 : Y=(F2-U2)*U2 : X=O1+X : Y=O1+Y : X=(O1+U2)-X : Y=O1-Y
2660 IF (X><O OR Y><O) THEN 2710
2670 X=(F2+U2)*U1 : Y=(F2-U2)*U1 : X=O1-X : Y=O1-Y : X=F9-X : Y=O1-Y
2680 IF (X><O OR Y><O) THEN 2710
2690 R3=F1-O2*R3 : PRINT "  R3=1:";A$;E$;B$
2700 IF (R3-G3=O1) THEN PRINT F$;A$;P$
2710 IF R3=F1 THEN PRINT A$;H$;C$;" nor ";B$
2720 S1=O1 : X=O1+F2*(O1+F2) : Y=(O1+U2)*F2 : Z=X-Y : T=Y-X : S=Z+T
2730 IF (S=0) THEN 2770
2740 S1=O : J3=J3+1
2750 PRINT "FLAW: Nonzero  (X-Y)+(Y-X) =";S;" when"
2760 PRINT "      X =";X;"  and  Y =";Y
2770 S=O : IF (G1*G2*G3<O1 OR R1<O1 OR R2<O1 OR R3<O1 OR INT(B2)><B2) THEN 2890
2780 PRINT : PRINT "Checking for sticky bit (S)."
2790 X=(F2+U1)*U2 : Y=F2*U2 : Z=O1+Y : T=O1+X : IF (Z-O1>O OR T-O1<U2)THEN 2890
2800 Z=T+Y : Y=Z-X : IF (Z-T<U2 OR Y-T><O) THEN 2890
2810 X=(F2+U1)*U1 : Y=F2*U1 : Z=O1-Y : T=O1-X : IF (Z-O1><O OR T-F9><O) THEN 2890
2820 Z=(F2-U1)*U1 : T=F9-Z : Q=F9-Y : IF (T-F9><O OR (F9-U1)-Q><O) THEN 2890
2830 Z=(O1+U2)*T5 : T=(T5+U2)-Z+U2 : X=O1+F2/B : Y=O1+B*U2 : Z=X*Y
2840 IF (T><O OR (X+B*U2)-Z><O) THEN 2890
2850 IF (B=O2) THEN 2870
2860 X=O2+U2 : Y=X/O2 : IF (Y-O1><O) THEN 2890
2870 S=S1
2880 IF (S=O1) THEN PRINT " S=1: Sticky bit";E$;"used correctly."
2890 IF (S=O) THEN PRINT " S=0: Sticky bit used incorrectly or not at all."
2900 IF (G1*G2*G3=O OR R1<O OR R2<O OR R3<O) THEN J3=J3+1
2910 L=60 : '=================================================================
2920 PRINT : PRINT "Does Multiplication commute?  Testing if  X*Y = Y*X  for";I0;"random pairs:"
2930 R9=SQR(3) : I=I0+1 : X9=O1/O3 : GOTO 2960
2940 ' ____  Random Number Generator  ____
2950 X=X9+R9 : Y=X*X : Y=Y*Y : X=X*Y : Y=X-INT(X) : X9=Y+X*.000005 : RETURN
2960 GOSUB 2950 : Y9=X9 : GOSUB 2950 : Z=X9*Y9 : Y=Y9*X9 : Z9=Z-Y : I=I-1 : IF (I>0 AND Z9=O) THEN 2960
2970 IF (I>0) THEN 3000
2980 X9=O1+F2/O3 : Y9=(U2+U1)+O1 : Z=X9*Y9 : Y=Y9*X9 : Z9=(O1+F2/O3)*((U2+U1)+O1)-((U2+U1)+O1)*(O1+F2/O3) : IF NOT (Z9=O) THEN 3000
2990 PRINT " **********  No failure found in ";I0;" randomly chosen pairs.  **********" : GOTO 3010
3000 J2=J2+1 : PRINT "DEFECT:   X*Y = Y*X  violated at  X = ";X9;", Y = ";Y9 : PRINT " X*Y =";Z;",  Y*X =";Y;",  X*Y-Y*X =";Z9 : PRINT "   ... pair no.";I0-I+1
3010 L=70 : '=================================================================
3020  PRINT : PRINT "Running tests of Square Root  SQR(X) :" : X=O : I=0
3030 Y=SQR(X) : IF (Y=X AND Y-F2=X-F2) THEN 3050
3040 J0=J0+1 : PRINT F$;V$;X;"= SQR(";X;"), miscalculated as";Y
3050 X=-X : I=I+1 : IF (I=1) THEN 3030
3060 X=O1 : I=I+1 : IF (I=3) THEN 3030
3070 E5=O : E7=O : GOTO 3150 : ' ... record min and max errors.
3080 ' ____ Subroutine to assess error  SQRT(X*X)-X  in Ulps. ____
3090 E6=((SQR(X*X)-X*B1)-(X-X*B1))/U : IF (E6=O) THEN RETURN
3100 IF (E6<E5) THEN E5=E6
3110 IF (E6>E7) THEN E7=E6
3120  PRINT : J=J+1 : PRINT Z$;"DEFECT :  SQR(";X*X;") - ";X;" = ";U*E6 : PRINT "         instead of correct value  0 ." : RETURN
3130 ' ---- End of Sqrt(X*X)-X subroutine. ----
3140 ' Test whether SQRT(X*X) = X ...
3150 J=0 : Z$=S$ : X=B : U=U2 : GOSUB 3090
3160 X=B1 : U=B1*U1 : GOSUB 3090
3170 X=W : U=O1 : GOSUB 3090
3180 X=U1 : U=U1*U1 : GOSUB 3090
3190 IF (J=0) THEN 3210
3200 J1=J1+J : GOSUB 110 : ' If SQRT has SERIOUS DEFECTS, then PAUSE ----
3210 PRINT "Testing if  SQR(X*X) = X  for  ";I0;" integers  X";
3220 J=0 : Z$="" : X=O2 : Y=B : IF (B=O1) THEN 3240
3230 X=Y : Y=B*X : IF (Y-X<I0) THEN 3230
3240 U=X*U2 : FOR I=1 TO I0
3250 X=X+O1 : GOSUB 3090 : IF (J>0) THEN 3280
3260 NEXT I
3270 PRINT "  found no discrepancies." : GOTO 3290
3280 J2=J2+J
3290  ' Test SQRT for monotonicity.
3300 I=-1 : X=B9 : Y=B : Z=B+B*U2
3310 I=I+1 : X=SQR(X) : Q=SQR(Y) : Z=SQR(Z) : IF NOT (X>Q OR Q>Z) THEN 3330
3320 J2=J2+1 : PRINT "DEFECT:  SQR(X) is non-monotonic for  X  near ";Y : GOTO 3390
3330 Q=INT(Q+F2) : IF NOT (I>0 OR Q*Q=B) THEN 3380
3340 IF (I>0) THEN 3360
3350 Y=Q : X=Y-U2 : Z=Y+U2 : GOTO 3310
3360 IF (I>1) THEN 3380
3370 Y=Y*B1 : X=Y-U1 : Z=Y+U1 : GOTO 3310
3380 PRINT "SQR has passed a test for Monotonicity."
3390 L=80 : ' Test SQRT for accuracy ...=====================================
3400 E5=E5+F2 : E7=E7-F2 : ' e5=min{error+1/2}, e7=max{error-1/2}
3410 Y=(SQR(O1+U2)-O1)/U2 : E6=(Y-O1)+U2/O8 : IF (E6>E7) THEN E7=E6
3420 E6=Y+U2/O8 : IF (E6<E5) THEN E5=E6
3430 Y=((SQR(F9)-U2)-(O1-U2))/U1 : E6=Y+U1/O8 : IF (E6>E7) THEN E7=E6
3440 E6=(Y+O1)+U1/O8 : IF (E6<E5) THEN E5=E6
3450 I=0 : U=U2 : X=U
3460 I=I+1 : Y=SQR((X+U1+X)+F9) : Y=((Y-U2)-((O1-U2)+X))/U : Z=((U1-X)+F9)*F2*X*X/U : E6=(Y+F2)+Z : IF (E6<E5) THEN E5=E6
3470  E6=(Y-F2)+Z : IF (E6>E7) THEN E7=E6
3480 ON I GOTO 3500, 3520, 3500, 3530 : ' Case statement
3490 ' Cases  I = 1 and 3
3500 X=U*SGN(X)*INT( O8/(O9*SQR(U)) ) : GOTO 3460
3510 ' Case  I = 2
3520 U=U1 : X=-U : GOTO 3460
3530 L=85 : ' Case  I = 4 exits  ..... =====================================
3540 IF (B=O1) THEN 3900
3550 PRINT"Testing whether  SQR  is rounded or chopped:"
3560 D=INT(F2+B^(O1+P-INT(P))) : ' ... = B^(1+fract)  if  P = integer + fract.
3570 X=D/B : Y=D/A1 : IF NOT (X=INT(X) AND Y=INT(Y)) THEN 3700
3580 X=O : Z2=X : Y=O1 : Y2=Y : Z1=B-O1 : D4=O4*D
3590 'Loop: for  Y = 1, 3, 5, ...  maximize  Y2 = Y*Y mod 4D .
3600 IF NOT (Y2>Z2) THEN 3650
3610 Q=B : Y1=Y : ' ... if new Y2 > old, check that  GCD(Y,B) = 1
3620 X1=ABS(Q+INT(F2-Q/Y1)*Y1) : Q=Y1 : Y1=X1 : IF (X1>O) THEN 3620
3630 IF (Q>O1) THEN 3650 : ' If GCD(Y,B) > 1 then skip over Y ;  else ...
3640 Z2=Y2 : Z=Y : ' ... and GCD(Z, B) =1
3650 Y=Y+O2 : X=X+O8 : Y2=Y2+X : IF NOT (Y2<D4) THEN Y2=Y2-D4 : '...= Y*Y mod 4D
3660 IF (Y<D) THEN 3600 : ' else  0 < Z < D  &  Z2 = Z^2 mod 4D  is maximal.
3670 X8=D4-Z2 : Q=(X8+Z*Z)/D4 : X8=X8/O8 : IF NOT (Q=INT(Q)) THEN 3700
3680 X=Z1*Z : X=X-INT(X/B)*B : IF (X=O1) THEN 3800 : ' with  1 = Z*Z1 mod B
3690 Z1=Z1-O1 : IF (Z1>O) THEN 3680 : ' else Failure!
3700 J0=J0+1 : PRINT F$;" Anomalous arithmetic with integers < B^P =";W : PRINT "         foils test whether  SQR  rounds or chops." : GOTO 3940
3710 ' This subroutine puts  NewD = B*D  and  NewZ^2 mod NewD  =  Z^2 mod D
3720 X=Z1*Q : X=INT(F2-X/B)*B+X : Q=(Q-X*Z)/B+X*X*(D/B) : Z=Z-O2*X*D : IF (Z>O) THEN 3740
3730 Z=-Z : Z1=-Z1
3740 D=B*D : RETURN : ' ___ end of NewD subroutine.___
3750 'This Subroutine tests if SQRT(D*X)=SQRT((Y-1/2)^2+X8/2) rounds to  Y .__
3760 IF (X-B<Z2-B OR X-Z2>W-Z2) THEN RETURN
3770 I=I+1 : X2=SQR(X*D) : Y2=(X2-Z2)-(Y-Z2) : X2=X8/(Y-F2) : X2=X2-F2*X2*X2 : E6=(Y2+F2)+(F2-X2) : IF (E6<E5) THEN E5=E6
3780 E6=Y2-X2 : IF (E6>E7) THEN E7=E6
3790 RETURN : ' ____ End of subroutine to test  SQRT(D*X) = Y . ____
3800 IF (Z1>B2) THEN Z1=Z1-B : '  -B/2 <= Z1 = 1/Z mod B <= B/2
3810 GOSUB 3720 : IF (U2*D<F9) THEN 3810 : ' ... until  D = B^(P-1) .
3820 IF NOT (D*B-D=W-D) THEN 3700
3830 Z2=D : I=0 : ' Count how many tests of SQRT(D*X)=Y yield results.
3840 Y=D+(O1+Z)*F2 : X=D+Z+Q : GOSUB 3750
3850 Y=D+(O1-Z)*F2+D : X=D-Z+D : X=X+Q+X : GOSUB 3750
3860 GOSUB 3720 : IF NOT (D-Z2=W-Z2) THEN 3700
3870 Y=(D-Z2)+(Z2+(O1-Z)*F2) : X=(D-Z2)+(Z2-Z+Q) : GOSUB 3750
3880 Y=(O1+Z)*F2 : X=Q : GOSUB 3750
3890 IF (I=0) THEN 3700
3900 IF (E5<0 OR E7>0) THEN 3920
3910 R4=O1 : PRINT Q$;E$;B$ : GOTO 3960
3920 IF (E7+U2>U2-F2 OR E5>F2 OR E5+B<F2) THEN 3940
3930 R4=O : PRINT Q$;E$;C$;"." : GOTO 3960
3940 PRINT Q$;H$;C$;" nor ";B$ : PRINT "Observed errors run from  ";E5-F2;"  to  ";F2+E7;" ulps." : IF (E7-E5<B*B) THEN 3960
3950 J1=J1+1 : PRINT S$;"DEFECT:  SQR";I$
3960 L=90 : GOSUB 110 : ' ---- PAUSE ---- ===================================
3970 PRINT "Testing powers  Z^i  for small integers  Z  and  i :" : GOTO 4120
3980 ' ___  Subroutine to compare  Z^I  with  X = Z*Z*...*Z  ( I times )  ___
3990 Y=Z^I : Q=I : GOSUB 4040 : ' ... test whether  Y=X
4000 I=I+1 : IF (I>M) THEN RETURN : ' ... with  X = Z^M
4010 X=Z*X : IF (X<W) THEN 3990
4020 RETURN : ' ___ End of comparison  subroutine ___
4030 Y=Z^Q : ' ___ Subroutine to test if  Y = X  ___
4040 IF (Y=X) THEN 4080
4050 IF (N>0) THEN 4070
4060 J2=J2+1 : PRINT "DEFECT: Computed  (";Z;")^(";Q;") =";Y : PRINT "   compares Unequal to correct ";X;" ; they differ by  ";Y-X
4070 N=N+1 : ' ... counts discrepancies.
4080 RETURN : ' ___ End of test subroutine. ___
4090 ' ___ Subroutine to print count  N  of discrepancies. ___
4100 IF (N>0) THEN PRINT "Similar discrepancies have occurred ";N;" times."
4110 RETURN : ' ___ End of sub. ___
4120 N=0 : I=0 : Z=-O : M=3 : ' ... test powers of zero
4130 X=O1 : GOSUB 3980 : IF (I>10) THEN 4150
4140 I=1023 : GOSUB 3980
4150 IF (Z=F1) THEN 4170 : ' ... If (-1)^n is invalid, replace  F1  by  O1  ...
4160 Z=F1 : I=-4 : GOTO 4130
4170 GOSUB 4090 : ' ... print  N  if  N>0.
4180 N1=N : N=0 : Z=A1 : M=INT( O2*LOG(W)/LOG(A1) )
4190 X=Z : I=1 : GOSUB 3980 : IF (Z=A) THEN 4210
4200 Z=A : GOTO 4190
4210 L=100 : ' Powers of radix  B  have been tested; next try a few primes: ==
4220 M=I0 : Z=O3
4230 X=Z : I=1 : GOSUB 3980
4240 Z=Z+O2 : IF (O3*INT(Z/O3) = Z) THEN 4240
4250 IF (Z<O8*O3) THEN 4230
4260 IF (N>0) THEN PRINT "Error like this may invalidate financial calculations involving interest rates."
4270 N=N+N1 : GOSUB 4280 : GOTO 4330
4280 GOSUB 4090 : ' ... print  N  if  N>0.
4290 IF (N=0) THEN PRINT "  ... no discrepancies found."
4300 PRINT
4310 IF (N>0) THEN  GOSUB 110 : ' ---- PAUSE ----
4320 RETURN : ' ___ End of printing sub. ___
4330 L=110 : PRINT "Seeking Underflow thresholds  U0  and  E0 :" : '==========
4340 D=U1 : IF(P=INT(P)) THEN 4370
4350 D=B1 : X=P
4360 D=D*B1 : X=X-O1 : IF (X>O) THEN 4360
4370 Y=O1 : Z=D : ' ... D = a power of  1/B < 1
4380 C=Y : Y=Z : Z=Y*Y : IF (Y>Z AND Z+Z>Z) THEN 4380
4390 Y=C : Z=Y*D
4400 C=Y : Y=Z : Z=Y*D : IF (Y>Z AND Z+Z>Z) THEN 4400
4410 H1=B : IF (H1<O2) THEN H1=O2
4420 H=O1/H1 : '  ... 1/H1 = H = min{ 1/B, 1/2 }
4430 C1=O1/C :E0=C : Z=E0*H : ' ... C = 1/B^(big integer) << 1 << C1 = 1/C
4440 Y=E0 : E0=Z : Z=E0*H : IF (E0>Z AND Z+Z>Z) THEN 4440
4450 U0=E0 : E1=O : Q=O : E9=U2 :S1=O1+E9 : D=C*S1 : IF (D>C) THEN 4490
4460 E9=B*U2 : S1=O1+E9 : D=C*S1 : IF (D>C) THEN 4490
4470 PRINT F$;M$;I$ : ' ... Multiplication is too crude
4480 J0=J0+1 : T0=E0 : Y1=O : Z0=Z : GOSUB 110 : GOTO 4570
4490 T0=D : Z0=T0*H : U0=O
4500 Y1=T0 : T0=Z0 : IF (E1+E1>E1) THEN 4520
4510 Y2=T0*H1 : E1=ABS(Y1-Y2) : Q=Y1 : IF (U0=O AND Y1><Y2) THEN U0=Y1
4520 Z0=T0*H : IF (T0>Z0 AND Z0+Z0>Z0) THEN 4500
4530 ' Now  1 >> C=1/B^(integer)  >=   Y    >   E0=Y*H   >~ Z:=E0*H >~ 0 ,
4540 ' and  1 >> D=(1+E9)*C >= U0 >= Q >= Y1 > T0:=Y1*H >~ Z0:=T0*H >~ 0 ,
4550 ' and  U0 = D/B^integer  is first to violate  (U0*H)/H=U0 , else  U0=0 ;
4560 ' and  Q:=U0/B^integer  is first with  E1 := |(Q*H)/H - Q| > 0, else Q=Y1.
4570 IF (Z0=O) THEN 4860
4580 ' ... Test  Z0  for "phoney-zero" violating  Z0<T0 or Z0<Z0+Z0  ...
4590 PRINT : Z=Z0 : Z$="Z0" : IF (Z0>O) THEN 4620
4600 J0=J0+1 : PRINT "FAILURE:  Positive expressions can underflow to an allegedly negative value" : PRINT "          Z0  that prints out as "; Z0 : X=-Z0 : IF (X>0) THEN 4630
4610 PRINT "          But  -Z0 , which should then be positive, isn't; it prints out as", X : GOTO 4630
4620 J3=J3+1 : PRINT "FLAW:  Underflow can stick at an allegedly positive value  Z0" : PRINT "       that prints out as "; Z0
4630 GOSUB 4640 : GOTO 4860 : ' ... end of test for "phoney-zero".
4640 '___ Subroutine to test  Z & Z$  for Partial Underflow ___
4650 N=0 : IF (Z=0) THEN RETURN
4660 PRINT "Since Comparison denies  ";Z$;" = 0 , evaluating  (";Z$;"+";Z$;")/";Z$;"  should be safe;" : PRINT "what the machine gets for  (";Z$;"+";Z$;")/";Z$;"  is   "; : Q9=(Z+Z)/Z : PRINT Q9 : IF (ABS(Q9-O2)<B*U2) THEN 4750
4670 IF (Q9<O1 OR Q9>O2) THEN 4740
4680 N=1 : J2=J2+1 : PRINT "This is a DEFECT." : PRINT : GOTO 4760
4690 ' ___ Subroutine to test  Z & Z$ for Partial Overflow ___
4700 N=0 : PRINT "Since Comparison alleges ";Z$;" =";Z;" is finite" : PRINT "and nonzero, the next two expressions should not over/underflow:" : V9=Z*F2
4710 PRINT "The machine computes  (0.5*";Z$;")/";Z$;" ="; : Q9=V9/Z : PRINT Q9
4720 PRINT "The machine computes  ";Z$;"/(0.5*";Z$;") ="; : V9=Z/V9 : PRINT V9
4730 IF (ABS(Q9-F2)<U2 AND ABS(V9-O2)<B*U2) THEN 4750
4740 N=1 : J1=J1+1 : PRINT "This is a VERY SERIOUS DEFECT." : PRINT : GOTO 4760
4750 PRINT "  This is O.K. provided Over/Underflow has NOT just been signaled."
4760 V9=Z*O1 : X9=V9 : V9=O1*Z : Y9=V9 : V9=Z/O1 : IF (Z=X9 AND Z=Y9 AND Z=V9) THEN 4840
4770 N=1 : J2=J2+1
4780  PRINT "DEFECT:  What prints as  ";Z$;" =";Z;" compares different from"
4790 IF NOT (Z=X9) THEN PRINT "           ";Z$;"*1 = ";X9
4800 IF NOT (Z=Y9 OR Y9=X9) THEN PRINT "           1*";Z$;" = ";Y9
4810 IF NOT (Z=V9) THEN PRINT "           ";Z$;"/1 = ";V9
4820 IF (Y9=X9) THEN 4840
4830 J2=J2+1 : PRINT "DEFECT:";M$;" does not commute; comparison alleges that" : PRINT "         1*";Z$;" =";Y9;"  differs from  ";Z$;"*1 =";X9
4840 IF (N>0) THEN GOSUB 110 : ' ---- PAUSE ----
4850 RETURN : ' end of test for Partial Over/Underflow
4860 L=120 : ' ==============================================================
4870 IF (C1*Y<=C1*Y1) THEN 4890 : ' ... as happens on most machines.
4880 S1=H*S1 : E0=T0 : ' = least positive no. on HP 3000
4890 IF (E1=0 OR E1=E0) THEN 4930
4900 IF (E1<E0) THEN 4920
4910 J2=J2+1 : PRINT "DEFECT: Differences underflow at a higher threshold than Products." : GOTO 4930
4920 J2=J2+1 : PRINT "DEFECT: Products underflow at a higher threshold than Differences." : IF (Z0=O) THEN E0=E1 : ' ... but not if pseudo-zeros exist.
4930 PRINT "Smallest strictly positive number found is  E0 ="; E0
4940 Z=E0 : Z$="E0" : GOSUB 4640 : T0=E0 : IF (N=1) THEN T0=Y : ' for CDC 7600
4950 I=4 : IF (E1=O) THEN I=3 : ' ...  I=1 if E1=0=U0  ,   I=2 if E1>0=U0  ,
4960 IF (U0=O) THEN I=I-2 : '     ...  I=3 if E1=0<U0  ,   I=4 if E1>0 & U0>0
4970 ON I GOTO 4980, 5090, 5010, 5130 : ' ... case statement
4980 U0=T0 : IF (C1*Q = (C1*Y)*S1) THEN 5010
4990 J0=J0+1 : U0=Y : PRINT F$;"Either accuracy deteriorates as numbers approach a threshold" : PRINT "U0 =";U0;" coming down from  ";C;"," : PRINT "or else ";M$;I$ : GOSUB 110
5000 ' ___ Test for  X-Z = 0  although  X >< Z ___
5010 PRINT : R=SQR(T0/U0) : IF (R>H) THEN 5030
5020 Z=R*U0 : X=Z*(O1+R*H*(O1+H)) : GOTO 5040
5030 Z=U0 : X=Z*(O1+H*H*(O1+H))
5040 IF (X=Z OR X-Z><O) THEN 5080
5050 J3=J3+1 : PRINT "FLAW:  X =";X;" is Unequal to  Z =";Z;" ," : PRINT "      yet  X-Z  yields "; : Z9=X-Z : PRINT Z9;".  Should this NOT signal Underflow,"
5060 PRINT "this is a SERIOUS DEFECT that causes confusion when innocent statements like" : PRINT "        if (X=Z) then  ...  else  ... ( f(X)-f(Z) )/(X-Z) ..."
5070 PRINT "encounter Division by Zero although actually  X/Z = 1 + "; (X/Z-F2)-F2 : PRINT
5080 GOTO 5160 : ' ... end of test for  X-Z = 0  &  X >< Z
5090 ' Case I=2 : U0 = 0 < E1  !
5100 J0=J0+1 : PRINT F$;" Underflow confuses Comparison, which alleges that  Q = Y " : PRINT "         while denying that  |Q-Y| = 0 ; these values print out as" : PRINT "Q =";Q;",  Y =";Y2;",  |Q-Y| =";ABS(Q-Y2);" ,"
5110 PRINT "and  Q/Y = 1 + "; (Q/Y2-F2)-F2
5120 U0=Q : GOTO 5010
5130 ' Case I=4 ;  U0 > 0  &  E1 > 0
5140 IF NOT (Q=U0 AND E1=E0 AND ABS(U0-E1/E9)<=E1) THEN 5010
5150 PRINT "Underflow is Gradual; it incurs  Absolute error = (roundoff in U0) < E0." : Y=E0*C1 : Y=Y*(T5+U2) : X=C1*(O1+U2) : Y=Y/X : I3=0 : IF (Y=E0) THEN I3=1 : ' ... I3=1 unless gradual underflows are doubly rounded.
5160 PRINT "The  Underflow threshold  U0 is ";U0;" , below which" : PRINT "calculation may suffer larger  Relative error  than merely roundoff."
5170 Y2=U1*U1 : Y=Y2*Y2 : Y2=Y*U1 : IF (Y2>U0) THEN 5220
5180 IF (Y>E0) THEN 5200
5190 J1=J1+1 : I=4 : PRINT S$; : GOTO 5210
5200 J2=J2+1 : I=5
5210 PRINT "DEFECT:  Range is too narrow;   U1^";I;"  underflows."
5220 L=130 : GOSUB 110 : ' ---- PAUSE ---- ==================================
5230 Y=-INT(F2-T8*LOG(U0)/LOG(H1))/T8 : Y2=Y+Y
5240 PRINT "Since Underflow occurs below the threshold  U0 = (";H1;")^(";Y;") ," : PRINT "only underflow should afflict the expression     (";H1;")^(";Y2;") ;" : PRINT "actually calculating it yields   ";
5250 V9=H1^(Y2) : PRINT V9 : IF (V9>=O AND V9<=(B+B*E9)*U0) THEN 5270
5260 J1=J1+1 : PRINT S$; : GOTO 5300
5270 IF (V9>U0*(O1+E9)) THEN 5290
5280 PRINT "  This computed value is  O.K." : GOTO 5310
5290 J2=J2+1
5300 PRINT " DEFECT: this is not between 0 and  U0 =";U0
5310 L=140 : PRINT : ' ======================================================
5320 'Calculate  E2 = exp(2) = 7.389056099...
5330 X=O : I=2 : Y=O2*O3 : Q=O : N=0
5340 Z=X : I=I+1 : Y=Y/(I+I) : R=Y+Q : X=Z+R : Q=(Z-X)+R : IF (X>Z) THEN 5340
5350 Z=(T5+O1/O8)+X/(T5*T2) : X=Z*Z : E2=X*X : X=F9 : Y=X-U1
5360 PRINT "Testing  X^((X+1)/(X-1))  vs.  exp(2) = ";E2;"  as  X -> 1."
5370 FOR I=1 TO I0
5380 Z=X-B1 : Z=(X+O1)/(Z-(O1-B1)) : Q=X^Z-E2 : IF (ABS(Q)>T8*U2) THEN 5420
5390 Z=(Y-X)*O2+Y : X=Y : Y=Z : IF (O1+(X-F9)*(X-F9)>O1) THEN NEXT I
5400 IF (X>O1) THEN 5440
5410 X=O1+U2 : Y=U2+U2+X : GOTO 5370
5420 N=1 : J2=J2+1 : PRINT "DEFECT:  Calculated  (1 + (";(X-B1)-(O1-B1);"))^(";Z;")" : PRINT "         differs from correct value by  ";Q
5430 PRINT "This much error may spoil financial calculations involving tiny interest rates." : GOTO 5450
5440 IF (N=0) THEN PRINT "Accuracy seems adequate."
5450 L=150 : PRINT : ' =======================================================
5460 PRINT "Testing powers  Z^Q  at four nearly extreme values:" : N=0 : Z=A1 : Q=INT(F2-LOG(C)/LOG(A1))
5470 X=C1 : GOSUB 4030 : Q=-Q : X=C : GOSUB 4030 : IF (Z<O1) THEN 5490
5480 Z=A : GOTO 5470
5490 GOSUB 4280 : ' ... print count of discrepancies.
5500 L=160 : GOSUB 110 : ' ---- PAUSE ---- ===================================
5510 PRINT "Searching for Overflow threshold:"
5520 Y=-C1 : V9=H1*Y
5530 V=Y : Y=V9 : V9=H1*Y : IF (V9<Y) THEN 5530
5540 Z=V9 : PRINT "Can ` Z = -Y ' overflow?  Trying it on  Y =";Y; : V9=-Y : V0=V9 : IF (V-Y=V+V0) THEN 5560
5550 J3=J3+1 : PRINT " finds a" : PRINT "FLAW:  -(-Y) differs from Y" : GOTO 5570
5560 PRINT " seems O.K."
5570 IF (Z=Y) THEN 5590
5580 J1=J1+1 : PRINT S$;"DEFECT: Overflow past ";Y;"  shrinks to ";Z
5590  Y=V*(H1*U2-H1) : Z=Y+((O1-H1)*U2)*V : IF (Z<V0) THEN Y=Z
5600 IF (Y<V0) THEN V=Y
5610 IF(V0-V<V0) THEN V=V0
5620 PRINT "Overflow threshold is   V = ";V
5630 PRINT "Overflow saturates at  V0 = ";V0
5640 PRINT "No overflow should be signaled for  V*1 = "; : V9=V*O1 : PRINT V9 : PRINT "                           nor for  V/1 = "; : V9=V/O1 : PRINT V9 : PRINT "Any overflow signal separating this  *  from one above or below is a DEFECT."
5650 L=170 : ' ===============================================================
5660 IF (-V<V AND -V0<V0 AND -U0<V AND U0<V) THEN 5680
5670 J0=J0+1 : PRINT F$;" Comparisons are confused by Overflow."
5680 L=175 : '================================================================
5690 PRINT : I=0 : Z=U0
5700 I=I+1 : IF (Z=O) THEN 5770
5710 V9=SQR(Z) : Y=V9*V9 : IF NOT (Y/(O1-B*E9)<Z OR Y>(O1+B*E9)*Z) THEN 5770
5720 IF (V9>U1) THEN 5750
5730 Z$="" : J2=1+J2 : GOTO 5760
5740 PRINT Z$;"DEFECT:  Comparison alleges that what prints as  Z = ";Z : PRINT "                 is too far from  SQR(Z)^2 = ";Y : RETURN
5750 Z$=S$ : J1=1+J1
5760 GOSUB 5740
5770 ON I GOTO 5780, 5790, 5800
5780 Z=E0 : GOTO 5700
5790 Z=Z0 : GOTO 5700
5800 I=0 : Z=V
5810 L=180 : '=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*
5820 IF (B><2 OR P><56 OR Z0=0 OR -O=O) THEN 5850
5830 J0=1+J0 : PRINT F$;" Attempts to evaluate  SQR(Overflow threshold V)  in Double Precision" : PRINT "in  BASIC  on the  IBM PC  display the word  ` Overflow '  and then" : PRINT "disable the Keyboard !  This is disastrous." : GOTO 5920
5840 '************************************************************************
5850 V9=SQR(Z) : X=(O1-B*E9)*V9 : V9=V9*X : IF NOT (V9<(O1-O2*B*E9)*Z OR V9>Z) THEN 5900
5860 Y=V9 : IF (X<W) THEN 5880
5870 Z$="" : J2=1+J2 : GOTO 5890
5880 Z$=S$ : J1=1+J1
5890 I=1 : GOSUB 5740
5900 IF (I=1) THEN 5920
5910 I=1 : Z=V0 : GOTO 5850
5920 PRINT " *   *   *   *   *   *   *   *   *   *"
5930 L=190 : GOSUB 110 : '---- PAUSE ---- ====================================
5940 X=U0*V : Y=B*B : IF (X*Y>= O1 AND X<=Y) THEN 5990
5950 IF (X*Y>=U1 AND X<=Y/U1)THEN 5970
5960 J2=J2+1 : PRINT "DEFECT: Badly "; : GOTO 5980
5970 J3=J3+1 : PRINT "FLAW: ";
5980 PRINT "unbalanced range;  U0*V =";X;" is too far from  1."
5990 L=200 : ' Test  X/X  vs.  1. ============================================
6000 FOR I=1 TO 5
6010 X=F9 : IF (I=2) THEN X=O1+U2
6020 IF (I=3) THEN X=V
6030 IF (I=4) THEN X=U0
6040 IF (I=5) THEN X=B
6050 Y=X : V9=(Y/X-F2)-F2 : IF (V9=0) THEN 6100
6060 X$="   X/X  differs from  1  when  X =" : IF (V9=-U1 AND I<5) THEN 6080
6070 J0=J0+1 : PRINT F$;X$;X : GOTO 6090
6080 J1=J1+1 : PRINT "SERIOUS DEFECT:  ";X$;X
6090 PRINT "          Instead,  X/X - 1/2 - 1/2 = ";V9 : PRINT
6100 NEXT I
6110 L=210 : ' ===============================================================
6120 PRINT : PRINT "What messages and/or values does Division by Zero produce?" : PRINT "    Trying to compute  1/0  produces ...  "; : Q9=O1/O : PRINT Q9 : PRINT "    Trying to compute  0/0  produces ...  "; : Q9=O/O : PRINT Q9
6130 L=220 : GOSUB 110 : ' ---- PAUSE ---- ===================================
6140 N$="The number of  " : T$=" The arithmetic diagnosed " : PRINT
6150 IF (J0>0) THEN PRINT N$;"FAILURES  encountered =          ";J0
6160 IF (J1>0) THEN PRINT N$;S$;"DEFECTS  discovered =    ";J1
6170 IF (J2>0) THEN PRINT N$;"DEFECTS  discovered =            ";J2
6180 IF (J3>0) THEN PRINT N$;"FLAWS  discovered =              ";J3
6190 IF (J0+J1+J2+J3>0) THEN 6270
6200 PRINT "No failures, defects nor flaws have been discovered."
6210 IF (R1+R2+R3+R4<O4) THEN 6260
6220 IF (S<O1 OR (B-O2)*(B-O9-O1)><O) THEN 6250
6230 Z$="854" : IF (B=O2 AND (P-O4*O3*O2)*(P-T7-T7+O1)=O) THEN Z$="754"
6240 PRINT "Rounding appears to conform to the proposed IEEE standard  p";Z$ : IF (I3=0) THEN PRINT "except possibly for Double Rounding during Gradual Underflow."
6250 PRINT T$;"appears to be Excellent! : go to 4550
6260 PRINT T$;"seems  Satisfactory." : GOTO 6310
6270 IF (J0+J1+J2=0 AND J3>0) THEN PRINT T$;"seems Satisfactory though flawed."
6280 IF (J0+J1=0 AND J2>0) THEN PRINT T$;"may be Acceptable despite inconvenient Defects."
6290 IF (J0+J1>0) THEN PRINT T$;"has unacceptable  Serious  Defects."
6300 IF (J0>0) THEN PRINT "Potentially fatal FAILURE may have spoiled this program's subsequent diagnoses."
6310 PRINT : PRINT "End of Test."
6320 END
6330 ' Glossary of Variables
6340 ' ~~~~~~~~~~~~~~~~~~~~~
6350 ' A1=first of {2, 10, B} for which  B = A1^(integer) ,  A=1/A1
6360 ' B=radix, B1=1/B, B2=B/2, B8=Q8orV8, B9=B-U2
6370 ' C=1/B^(large integer), C1=1/C
6380 ' D=C*(1+E9) or 1/B^(integer) or B^(P-integer), D4=4D
6390 ' E0=min positive, E1=..., E2=exp(2), E3=..., E5-1/2=minSQRerror,
6400 ' E6=SQRerror, E7+1/2=maxSQRerror, E8=V a priori, E9=?*U2
6410 ' F1=-1, F2=1/2, F3.=1/3, F9=1-U1
6420 ' G1=?guard*, G2=?guard/, G3=?guard-
6430 ' H=min{ 1/B, 1/2 }, H1=1/H
6440 ' I=scratch integer, I0=number of random trials X*Y=Y*X, I3=IEEE
6450 ' J=scratch, J0=#FAILUREs, J1=#SERIOUS DEFECTs, J2=#DEFECTs, J3=#FLAWs
6460 ' K=page no. of diagnosis
6470 ' L=Milestone passed in program
6480 ' M=upper bound for  i  in tests of  Z^i
6490 ' N=0 unless Partial Over/Underflow is uncovered, N1=...
6500 ' O=0, O1=1, O2=2, O3=3, O4=4, O8=8, O9=9
6510 ' P=precision.=#Bdigits; if B=1 then P=0
6520 ' Q=scratch, Q8=#(Div. by 0), Q9=potential Divide by Zero
6530 ' R=scratch, R1=?round*, R2=?round/, R3=?round+-, R9=sqrt(3)
6540 ' S=?sticky bit, S1=...
6550 ' T=scratch, T0=underflow, T2=32, T5=1.5, T7=27, T8=240
6560 ' U=1 ulp, U0=underflow threshold, U1=1-Next(1, 0), U2=Next(1, 2)-1
6570 ' V.=overflow threshold, V0=1/0, V8=#(Overflow), V9=potential Overflow
6580 ' W=1/U1=B^P
6590 ' X=scratch, X1=..., X8=((-Z*Z)mod4D)/8, X9=random
6600 ' Y=scratch, Y1=..., Y2=..., Y9=random
6610 ' Z=scratch, Z0=pseudozero, Z1=..., Z2=Z*Zmod4D, Z9=scratch
6620 ' A$="  Add/Subtract", B$="correctly rounded.", C$="chopped"
6630 ' D$="  Division", F$="FAILURE:", I$="  gets too many last digits wrong.",
6640 ' E$=" appears to be ", H$=" is neither ", L$=" lacks a Guard Digit, "
6650 ' M$="  Multiplication", N$="The number of  ", V$=" Violation of "
6660 ' P$=" test is inconsistent;  PLEASE  NOTIFY  THE  AUTHOR !"
6670 ' Q$="Square Root"
6680 ' S$="SERIOUS ", T$=" The arithmetic diagnosed ", X$=scratch, Z$=scratch
6690 '------------------------------------------------------------------