Module Name: src
Committed By: riastradh
Date: Thu Aug 1 02:06:31 UTC 2019
Modified Files:
src/lib/libc/gdtoa: Makefile.inc gdtoa_fltrnds.h gdtoaimp.h
Log Message:
Honour the floating-point rounding mode in floating-point formatting.
C99, Sec. 7.19.6.1 `The fprintf function', paragraph 13, p. 281:
(Recommended practice)
For e, E, f, F, g, and G conversions, if the number of significant
decimal digits is at most DECIMAL_DIG, then the result should be
correctly rounded. If the number of significant decimal digits is
more than DECIMAL_DIG but the source value is exactly
representable with DECIMAL_DIG digits, then the result should be
an exact representation with trailing zeros. Otherwise, the
source value is bounded by two adjacent decimal strings L < U,
both having DECIMAL_DIG significant idgits; the value of the
resultant decimal string D should satisfy L <= D <= U, _with the
extra stipulation that the error should have a correct sign for
the current rounding direction_. [emphasis added]
The gdtoa code base already supports respecting the floating-point
rounding mode, as long as we compile it with Honor_FLT_ROUNDS
defined. However, for this to work, fegetround must be available in
libc, which it is not currently -- the fenv logic is in libm.
Fortunately, we don't have to move all of fenv from libm to libc --
programs that do not link against libm don't have fesetround, so the
rounding mode is always the default (barring asm shenanigans that
bypass the API -- tough). So use a weak reference to fegetround; by
default, assume FE_TONEAREST if it is not defined.
To generate a diff of this commit:
cvs rdiff -u -r1.10 -r1.11 src/lib/libc/gdtoa/Makefile.inc
cvs rdiff -u -r1.1.1.1 -r1.2 src/lib/libc/gdtoa/gdtoa_fltrnds.h
cvs rdiff -u -r1.14 -r1.15 src/lib/libc/gdtoa/gdtoaimp.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/lib/libc/gdtoa/Makefile.inc
diff -u src/lib/libc/gdtoa/Makefile.inc:1.10 src/lib/libc/gdtoa/Makefile.inc:1.11
--- src/lib/libc/gdtoa/Makefile.inc:1.10 Thu Jan 16 20:31:42 2014
+++ src/lib/libc/gdtoa/Makefile.inc Thu Aug 1 02:06:31 2019
@@ -1,10 +1,14 @@
-# $NetBSD: Makefile.inc,v 1.10 2014/01/16 20:31:42 christos Exp $
+# $NetBSD: Makefile.inc,v 1.11 2019/08/01 02:06:31 riastradh Exp $
# gdtoa sources
.PATH: ${.CURDIR}/gdtoa
CPPFLAGS+=-I${.CURDIR}/gdtoa -I${.CURDIR}/locale
+.if ${MACHINE_ARCH} == "vax"
CPPFLAGS+=-DNO_FENV_H
+.else
+CPPFLAGS+=-DHonor_FLT_ROUNDS
+.endif
# machine-dependent directory must provide the following:
# arith.h gd_qnan.h
Index: src/lib/libc/gdtoa/gdtoa_fltrnds.h
diff -u src/lib/libc/gdtoa/gdtoa_fltrnds.h:1.1.1.1 src/lib/libc/gdtoa/gdtoa_fltrnds.h:1.2
--- src/lib/libc/gdtoa/gdtoa_fltrnds.h:1.1.1.1 Sat Mar 19 16:26:37 2011
+++ src/lib/libc/gdtoa/gdtoa_fltrnds.h Thu Aug 1 02:06:31 2019
@@ -1,4 +1,5 @@
- FPI *fpi, fpi1;
+ CONST FPI *fpi;
+ FPI fpi1;
int Rounding;
#ifdef Trust_FLT_ROUNDS /*{{ only define this if FLT_ROUNDS really works! */
Rounding = Flt_Rounds;
Index: src/lib/libc/gdtoa/gdtoaimp.h
diff -u src/lib/libc/gdtoa/gdtoaimp.h:1.14 src/lib/libc/gdtoa/gdtoaimp.h:1.15
--- src/lib/libc/gdtoa/gdtoaimp.h:1.14 Fri Apr 19 10:41:53 2013
+++ src/lib/libc/gdtoa/gdtoaimp.h Thu Aug 1 02:06:31 2019
@@ -1,4 +1,4 @@
-/* $NetBSD: gdtoaimp.h,v 1.14 2013/04/19 10:41:53 joerg Exp $ */
+/* $NetBSD: gdtoaimp.h,v 1.15 2019/08/01 02:06:31 riastradh Exp $ */
/****************************************************************
@@ -200,6 +200,9 @@ THIS SOFTWARE.
#include "gd_qnan.h"
#ifdef Honor_FLT_ROUNDS
#include <fenv.h>
+__weakref_visible int __libc_fegetround_ref(void) __weak_reference(fegetround);
+#define fegetround() \
+ (__libc_fegetround_ref ? __libc_fegetround_ref() : FE_TONEAREST)
#endif
#ifdef DEBUG
