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| author | Szabolcs Nagy <nsz@port70.net> | 2012-11-13 10:30:40 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <nsz@port70.net> | 2012-11-13 10:30:40 +0100 |
| commit | 666271c105e4137bdfa195e217799d74143370d4 (patch) | |
| tree | 0caee4a6641171b1de1577266f9329b9eec5df38 | |
| parent | 662ed2006568f953290f5e0b40cce38252db78f4 (diff) | |
| download | musl-666271c105e4137bdfa195e217799d74143370d4.tar.gz | |
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)
| -rw-r--r-- | src/math/scalbn.c | 17 | ||||
| -rw-r--r-- | src/math/scalbnf.c | 17 |
2 files changed, 24 insertions, 10 deletions
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; } diff --git a/src/math/scalbnf.c b/src/math/scalbnf.c index 243dafdf..e5c76db3 100644 --- a/src/math/scalbnf.c +++ b/src/math/scalbnf.c @@ -2,6 +2,8 @@ float scalbnf(float x, int n) { + /* make sure result is stored as double on overflow or underflow */ + volatile float z; float scale; if (n > 127) { @@ -10,8 +12,10 @@ float scalbnf(float x, int n) if (n > 127) { x *= 0x1p127f; n -= 127; - if (n > 127) - return x * 0x1p127f; + if (n > 127) { + z = x * 0x1p127f; + return z; + } } } else if (n < -126) { x *= 0x1p-126f; @@ -19,10 +23,13 @@ float scalbnf(float x, int n) if (n < -126) { x *= 0x1p-126f; n += 126; - if (n < -126) - return x * 0x1p-126f; + if (n < -126) { + z = x * 0x1p-126f; + return z; + } } } SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23); - return x * scale; + z = x * scale; + return z; } |