Q37459: "pascal" Attribute for Multi-Thread Functions Returning Double

Article: Q37459
Product(s): See article
Version(s): 5.10
Operating System(s): OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 22-NOV-1988

Although it is not documented, an important requirement for returning
floating-point values from functions in a multi-thread environment is
defining and prototyping functions with the "pascal" function
attribute as we have done for all functions prototyped to return a
double in \include\mt\math.h.

When you use the pascal attribute on floating-point functions, the
floating-point return value is placed on the calling thread's stack,
providing each thread with its own return value as desired.

When using the default of the C function call/return convention
instead of pascal, we use a global variable __fac (floating-point
accumulator) for returning floating-point values. For multi-thread
applications or DLL's using CRTLIB.DLL, the global variable __fac
could be unintentionally modified by another thread, so it is not
contained in CRTEXE.OBJ, CRTDLL.OBJ, or CRTDLL.LIB. Consequently,
references to __fac will be unresolved at link time.

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