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Define TS 18661-1 CR_DECIMAL_DIG in <float.h>.

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TS 18661-1 defines a macro CR_DECIMAL_DIG in <float.h>, for the number
of decimal digits for which conversions between decimal character
strings and (IEEE) binary formats, in both directions, are correctly
rounded.  This patch implements support for this macro in GCC's
<float.h>.

The definition __UINTMAX_MAX__ is the right one for GCC's conversions
of floating constants, since I made those use MPFR to make them
correctly rounding.  The macro also covers standard library functions
such as strtod and printf.  The definition is also correct for current
glibc.  If any targets' libcs support correct rounding in a way that
conforms to TS 18661-1 with a smaller value of CR_DECIMAL_DIG, making
<float.h> reflect that could not be done in isolation without changes
to the interpretation of floating constants as well, since a smaller
CR_DECIMAL_DIG requires double rounding of floating constants (first
to CR_DECIMAL_DIG decimal digits, then to the desired binary format).

Boostrapped with no regressions on x86_64-pc-linux-gnu.

gcc:
	* ginclude/float.h [__STDC_WANT_IEC_60559_BFP_EXT__]
	(CR_DECIMAL_DIG): New macro.

gcc/testsuite:
	* gcc.dg/cr-decimal-dig-1.c: New test.

From-SVN: r240249
This commit is contained in:
Joseph Myers 2016-09-19 22:53:30 +01:00 committed by Joseph Myers
parent 63012d9a57
commit 1f2071fafd
4 changed files with 30 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2016-09-19 Joseph Myers <joseph@codesourcery.com>
* ginclude/float.h [__STDC_WANT_IEC_60559_BFP_EXT__]
(CR_DECIMAL_DIG): New macro.
2016-09-19 Joseph Myers <joseph@codesourcery.com>
* ginclude/stddef.h (max_align_t) [__i386__]: Add __float128

7
gcc/ginclude/float.h
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@ -185,6 +185,13 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
#endif /* C11 */
#ifdef __STDC_WANT_IEC_60559_BFP_EXT__
/* Number of decimal digits for which conversions between decimal
character strings and binary formats, in both directions, are
correctly rounded. */
#define CR_DECIMAL_DIG __UINTMAX_MAX__
#endif
#ifdef __STDC_WANT_IEC_60559_TYPES_EXT__
/* Constants for _FloatN and _FloatNx types from TS 18661-3. See
comments above for their semantics. */

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2016-09-19 Joseph Myers <joseph@codesourcery.com>
* gcc.dg/cr-decimal-dig-1.c: New test.
2016-09-19 Joseph Myers <joseph@codesourcery.com>
* gcc.dg/float128-align.c, gcc.dg/float128x-align.c,

14
gcc/testsuite/gcc.dg/cr-decimal-dig-1.c Normal file
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@ -0,0 +1,14 @@
/* Test TS 18661-1 CR_DECIMAL_DIG. */
/* { dg-do compile } */
/* { dg-options "-std=c11" } */
#define __STDC_WANT_IEC_60559_BFP_EXT__
#include <float.h>
#ifndef CR_DECIMAL_DIG
#error "CR_DECIMAL_DIG not defined"
#endif
#if CR_DECIMAL_DIG < DECIMAL_DIG + 3
#error "CR_DECIMAL_DIG too small"
#endif