PRB: Result Differs Between 16-bit and 32-bit _gcvt() (119504)
The information in this article applies to:
- The C Run-Time (CRT), when used with:
- Microsoft Visual C++, 32-bit Enterprise Edition
- Microsoft Visual C++, 32-bit Professional Edition
- Microsoft Visual C++, 32-bit Learning Edition
This article was previously published under Q119504 SYMPTOMS
Using the following test case, 32-bit _gcvt() returns a different value
than 16-bit _gcvt():
double r1 = 1.797693134862315E+308;
char buf[40];
_gcvt(r1, 15, buf);
The 16-bit _gcvt() rounds the value to 1.79769313486232E+308, but the
32-bit _gcvt() truncates the value to 1.79769313486231E+308.
CAUSE
The low-level floating-point-to-string conversion routines were completely
rewritten for Win32. The 32-bit output routines use an internal 12-byte
floating-point format for the intermediate values and a new conversion
algorithm. The specific value used in the test case mentioned in the
"SYMPTOMS" section is at the limit of type "double," and the new conversion
routine exhibits this problem when converting the value to a 12-byte value.
The conversion routine yields a mantissa string of 79769313486231490
instead of 797693134862315, which causes the rounding problems in this
particular case.
| Modification Type: | Major | Last Reviewed: | 12/1/2003 |
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| Keywords: | kbCRT kbprb KB119504 |
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