FIX: MASM Fails to Generate Error When Real Values Are Too Smal

Last reviewed: September 11, 1997
Article ID: Q72791

5.10 5.10a 6.00 6.00a 6.00b | 5.10 5.10a 6.00 6.00a 6.00b

MS-DOS                      | OS/2

kbtool kbfixlist kbbuglist

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 5.1, 5.1a, 6.0, 6.0a, and 6.0b
Microsoft Macro Assembler for OS/2, versions 5.1, 5.1a, 6.0, 6.0a, and 6.0b

SYMPTOMS

The Microsoft Macro Assembler (MASM) may fail to generate an error when a floating-point value is outside the range of the minimum allowable values.

As documented on page 142 of the "Microsoft Macro Assembler Programmer's Guide" included with version 6.0, the limits when using the 4-byte REAL4 (or DD), 8-byte REAL8 (or DQ), or the 10-byte REAL10 (or DT) are as follows:

   Size        Low          High
   ----        ---          ----

   4 byte      1.18E-38     3.40E+38
   8 byte      2.23E-308    1.79E+308
  10 byte      3.37E-4932   1.18E+4932

However, MASM versions 5.1, 5.1a, 6.0, 6.0a, and 6.0b fail to generate an error when exceeding the low end of this range until a value of 3.37E-32752 or smaller for the 4 and 8-byte types and a value of 3.37E-32746 or smaller for the 10-byte type.

STATUS

Microsoft has confirmed this to be a problem in MASM versions 5.1, 5.1a, 6.0, 6.0a, and 6.0b. This problem was corrected in MASM for MS-DOS version 6.1.

MORE INFORMATION

The sample program below may be used to illustrate this problem. In the code, two of each of the 4-, 8-, and 10-byte data types are declared and initialized. For each type, one initializing value is used that correctly causes an error, while the other similar initializing value fails to cause an error, even though it should.

The declaration of n1, n3, and n5 correctly result in the following error in MASM version 6.0, 6.0a, and 6.0b:

   error A2071: initializer magnitude too large for specified size

MASM versions 5.1 and 5.1a are not as explicit in their error message, but they correctly generate the following overflow error for n1, n3, and n5:

   error A2029: division by 0 or overflow

Neither MASM version 5.1, 5.1a, 6.0, 6.0a, or 6.0b generates an error (as they should) on the declaration of n2, n4, and n6. (These versions fail to produce the expected error for any number smaller than the values listed above for each data type.)

Sample Code

; Assemble options needed: none

.MODEL large .STACK 4096

.DATA

n1 DD 1.18E-32752   ;Causes error
n2 DD 1.18E-32751   ;Should cause error, but doesn't
n3 DQ 2.23E-32752   ;Causes error
n4 DQ 2.23E-32751   ;Should cause error, but doesn't
n5 DT 3.37E-32746   ;Causes error
n6 DT 3.37E-32745   ;Should cause error, but doesn't

.CODE start:

   mov ax, 4C00h
   int 21h

END start

Additional reference words: 5.10 5.10a 6.00 6.00a 6.00b buglist6.00
buglist6.00a buglist6.00b fixlist6.10
KBCategory: kbtool kbfixlist kbbuglist
KBSubCategory: MLIss
Solution Type : kbfix

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Last reviewed: September 11, 1997
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