From 666271c105e4137bdfa195e217799d74143370d4 Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Tue, 13 Nov 2012 10:30:40 +0100 Subject: math: fix scalbn and scalbnf on overflow/underflow old code was correct only if the result was stored (without the excess precision) or musl was compiled with -ffloat-store. (see note 160 in n1570.pdf section 6.8.6.4) --- src/math/scalbn.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) (limited to 'src/math/scalbn.c') diff --git a/src/math/scalbn.c b/src/math/scalbn.c index c9c7af80..42a2b294 100644 --- a/src/math/scalbn.c +++ b/src/math/scalbn.c @@ -2,6 +2,8 @@ double scalbn(double x, int n) { + /* make sure result is stored as double on overflow or underflow */ + volatile double z; double scale; if (n > 1023) { @@ -10,8 +12,10 @@ double scalbn(double x, int n) if (n > 1023) { x *= 0x1p1023; n -= 1023; - if (n > 1023) - return x * 0x1p1023; + if (n > 1023) { + z = x * 0x1p1023; + return z; + } } } else if (n < -1022) { x *= 0x1p-1022; @@ -19,10 +23,13 @@ double scalbn(double x, int n) if (n < -1022) { x *= 0x1p-1022; n += 1022; - if (n < -1022) - return x * 0x1p-1022; + if (n < -1022) { + z = x * 0x1p-1022; + return z; + } } } INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0); - return x * scale; + z = x * scale; + return z; } -- cgit v1.2.1 From c4359e01303da2755fe7e8033826b132eb3659b1 Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Tue, 13 Nov 2012 10:55:35 +0100 Subject: math: excess precision fix modf, modff, scalbn, scalbnf old code was correct only if the result was stored (without the excess precision) or musl was compiled with -ffloat-store. now we use STRICT_ASSIGN to work around the issue. (see note 160 in c11 section 6.8.6.4) --- src/math/scalbn.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) (limited to 'src/math/scalbn.c') diff --git a/src/math/scalbn.c b/src/math/scalbn.c index 42a2b294..003141e3 100644 --- a/src/math/scalbn.c +++ b/src/math/scalbn.c @@ -2,8 +2,6 @@ double scalbn(double x, int n) { - /* make sure result is stored as double on overflow or underflow */ - volatile double z; double scale; if (n > 1023) { @@ -13,8 +11,8 @@ double scalbn(double x, int n) x *= 0x1p1023; n -= 1023; if (n > 1023) { - z = x * 0x1p1023; - return z; + STRICT_ASSIGN(double, x, x * 0x1p1023); + return x; } } } else if (n < -1022) { @@ -24,12 +22,12 @@ double scalbn(double x, int n) x *= 0x1p-1022; n += 1022; if (n < -1022) { - z = x * 0x1p-1022; - return z; + STRICT_ASSIGN(double, x, x * 0x1p-1022); + return x; } } } INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0); - z = x * scale; - return z; + STRICT_ASSIGN(double, x, x * scale); + return x; } -- cgit v1.2.1