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Add a macro STRICT_ASSIGN() to help avoid the compiler bug that

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assignments and casts don't clip extra precision, if any.  The
implementation is to assign to a temporary volatile variable and read
the result back to assign to the original lvalue.

lib/msun currently 2 different hard-coded hacks to avoid the problem
in just a few places and needs it in a few more places.  One variant
uses volatile for the original lvalue.  This works but is slower than
necessary.  Another temporarily casts the lvalue to volatile.  This
broke with gcc-4.2.1 or earlier (gcc now stores to the lvalue but
doesn't load from it).
This commit is contained in:
Bruce Evans 2008-01-17 17:02:11 +00:00
parent d2012f3333
commit 1880ccbd79
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=175403
1 changed files with 16 additions and 0 deletions
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16
lib/msun/src/math_private.h
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@ -154,6 +154,22 @@ do { \
(d) = sf_u.value; \
} while (0)
#ifdef FLT_EVAL_METHOD
/*
* Attempt to get strict C99 semantics for assignment with non-C99 compilers.
*/
#if FLT_EVAL_METHOD == 0 || __GNUC__ == 0
#define STRICT_ASSIGN(type, lval, rval) ((lval) = (rval))
#else
#define STRICT_ASSIGN(type, lval, rval) do { \
volatile type __lval; \
\
__lval = (rval); \
(lval) = __lval; \
} while (0)
#endif
#endif
/*
* Common routine to process the arguments to nan(), nanf(), and nanl().
*/