IF VAL(s$) <1 OR VAL(s$) > 3 (incorrect result?)

[md]


DEFINT A-Z
CLS
LastKey$ = "1"
PetCount = 3

IF VAL(LastKey$) < 1 OR VAL(LastKey$) > PetCount THEN
PRINT "THIS SHOULD NOT HAVE DISPLAYED"   'this is incorrect
END IF

TheVal = VAL(LastKey$)                    'correction
IF TheVal < 1 OR TheVal > PetCount THEN
 PRINT "THIS DOES NOT DISPLAY"          
END IF


[Jos]

When I run that code in PowerBasic 3.5 (by F9), I get a blank window.
Pressing a key returns to the PB editor.

Jos

[md]

This dump might be of interest

Offset  Data    Source Line           Microsoft (R) BASIC Compiler Version 7.10

0030   0006    DEFINT A-Z
0030   0006    CLS
0030    **        I00002:   jmp     I00003
0032    **        I00004:   pop     ax
0033    **                  push    di
0034    **                  push    si
0035    **                  push    cs
0036    **                  push    ax
0037    **                  jmp     B$SAS1
003C    **        I00005:   pop     ax
003D    **                  push    si
003E    **                  push    di
003F    **                  push    cs
0040    **                  push    ax
0041    **                  jmp     B$SCT1
0046   0006    LastKey$ = "1"
0046   0006    PetCount = 3
0046   0006    
0046   0006    IF VAL(LastKey$) < 1 OR VAL(LastKey$) > PetCount THEN
0046   0006     PRINT "THIS SHOULD NOT HAVE DISPLAYED"
0046   0006    END IF
0046    **        I00003:   push    0FFh
0048    **                  call    B$SCLS
004D    **                  mov     di,offset <const>
0050    **                  mov     si,offset LASTKEY$
0053    **                  call    I00004
0056    **                  mov     PETCOUNT%,0003h
005C    **                  int     39h
005E    **                  db      06h
005F    **                  dw      <000000000000F03F>
0061    **                  push    si
0062    **                  call    B$FVAL
0067    **                  mov     di,ax
0069    **                  int     39h
006B    **                  db      05h
006C    **                  int     3Dh
006E    **                  call    B$FCMP
0073    **                  jb      I00007
0075    **                  int     3Bh
0077    **                  db      06h
0078    **                  dw      PETCOUNT%
007A    **                  push    si
007B    **                  call    B$FVAL
0080    **                  mov     si,ax
0082    **                  int     39h
0084    **                  db      04h
0085    **                  int     3Dh
0087    **                  call    B$FCMP
008C    **                  jna     I00006
008E    **        I00007:   push    offset <const>
0091    **                  call    B$PESD
0096   000C    
0096   000C    TheVal = VAL(LastKey$)
0096   000C    IF TheVal < 1 OR TheVal > PetCount THEN
                                                                      PAGE   2
                                                                     20 Feb 24
                                                                     20:52:40
Offset  Data    Source Line           Microsoft (R) BASIC Compiler Version 7.10

0096   000C      PRINT "THIS DOES NOT DISPLAY"
0096   000C    END IF
0096    **        I00006:   push    offset LASTKEY$
0099    **                  call    B$FVAL
009E    **                  mov     si,ax
00A0    **                  int     39h
00A2    **                  db      04h
00A3    **                  int     3Bh
00A5    **                  db      1Eh
00A6    **                  dw      THEVAL%
00A8    **                  int     3Dh
00AA    **                  cmp     word ptr THEVAL%,01h
00AF    **                  jl      I00009
00B1    **                  mov     ax,PETCOUNT%
00B4    **                  cmp     ax,THEVAL%
00B8    **                  jnl     I00008
00BA    **        I00009:   push    offset <const>
00BD    **                  call    B$PESD
00C2   000E    
00C2    **        I00008:   call    B$CENP
00C7   000E    


[Jos]

It shows MS Basic compiled code seemingly uses its own floating point emulator unconditionally.
That is it doesn’t for instance execute opcode DDh which is redirected to INT 39h if a FPU is missing.
Instead INT 39h is executed directly.
However, could be compiled code does this for simple loading and retrieving the top FPU register, while library functions like B$FCMP in contrast do use FPU instructions.

The first test uses floating point values, the second binary values.
B$FCMP will return VAL("1") < 1? This mishap is with vDos 2023.05.01?

Jos

[Jos]

Could you post this compiled sample?

Jos

[md]

I don't know if executables can be posted. This is attempting to post "test2.exe". It worked!

Attachments:

test2.EXE (6.87 KB)

[Jos]

The program requires (at least) one extra file, I get:

C:\>test2
Input path for run-time module brt71enr.exe:

Jos

[md]

bc test2/o;
link test2;

As reference brt71enr.exe is 84,800 bytes 11/21/1992 09:30 AM

Attachments:

test2.EXE (24.5 KB)

[Jos]

Could you post that brt71enr.exe file?

Jos

[md]

Definitely.
I hope nothing else is needed. I didn't check.

Attachments:

brt71enr.exe (82.81 KB)

brt71enr.lib (36.19 KB)

[Jos]

With brt71enr.exe in place I also get:

C:\>test2
LESS
Will have a look at this...

Jos

[Jos]

I don’t expect those switches effect VAL("1") < 1.

g2 would enable some 32-bit CPU functions and direct access of extended memory?

RTLINK probably was faster that MS LINK and have some extra options.

Jos

[Jos]

I fixed this seemingly MS Basic specific issue, it didn’t directly relate to the involved test.

At startup MS Basic loads a predefined 80-bit floating point value into the FPU. The Windows MS runtime floating point libraries are however limited to 64-bit.
Shouldn’t generally be a problem, but the loaded value exceeds the 64-bit precision in a specific way.
Causing MS Basic to set a flag to do (unneeded) corrections later on. Exclusively(?) messing up that test.

Jos