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* lib/autoconf/c.m4 (AC_LANG_BOOL_COMPILE_TRY (C)): Use division by zero.

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Paul Eggert 2004-06-04 19:39:51 +00:00
parent 34638b0340
commit 8f94c94fe5
2 changed files with 20 additions and 4 deletions
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11
ChangeLog
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@ -1,3 +1,14 @@
2004-06-04 Paul Eggert <eggert@cs.ucla.edu>
* lib/autoconf/c.m4 (AC_LANG_BOOL_COMPILE_TRY (C)): Use division
by zero instead of array size, so that we can use any arithmetic
constant expression (instead of requiring an integer constant
expression). This allows us to test expressions like DBL_MAX <
LDBL_MAX, which didn't conform to the C standard using the old
method.
(AC_C_LONG_DOUBLE): Put back in the tests for LDBL_MAX and LDBL_EPSILON,
now that we can do floating-point tests at compile time.
2004-06-02 Paul Eggert <eggert@cs.ucla.edu>
* lib/autoconf/c.m4 (AC_C_LONG_DOUBLE): Don't check LDBL_MAX

13
lib/autoconf/c.m4
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@ -228,11 +228,14 @@ char (*f) () = $1;
# AC_LANG_BOOL_COMPILE_TRY(C)(PROLOGUE, EXPRESSION)
# -------------------------------------------------
# Be sure to use this array to avoid `unused' warnings, which are even
# errors with `-W error'.
# The C standard does not require a diagnostic when we compute 1 / 0
# at compile-time, but we don't know of any compiler that fails to
# diagnose this. Diagnostics are required for some other expressions
# (e.g., ((EXPRESSION) ? 0 : (0, 0)), INT_MAX + !!(EXPRESSION)),
# but they don't work as well in practice.
m4_define([AC_LANG_BOOL_COMPILE_TRY(C)],
[AC_LANG_PROGRAM([$1], [static int test_array @<:@1 - 2 * !($2)@:>@;
test_array @<:@0@:>@ = 0
[AC_LANG_PROGRAM([$1], [static int v = 1 / !!($2);
v = 0;
])])
@ -965,6 +968,8 @@ AC_DEFUN([AC_C_LONG_DOUBLE],
+ (DBL_MANT_DIG < LDBL_MANT_DIG)
- (LDBL_MAX_EXP < DBL_MAX_EXP)
- (LDBL_MANT_DIG < DBL_MANT_DIG)))
&& (0 < ((DBL_MAX < LDBL_MAX) + (LDBL_EPSILON < DBL_EPSILON)
- (LDBL_MAX < DBL_MAX) - (DBL_EPSILON < LDBL_EPSILON)))
&& (int) LDBL_EPSILON == 0
]])],
ac_cv_c_long_double=yes,