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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)
This commit is contained in:
Szabolcs Nagy 2012-11-13 10:30:40 +01:00
parent 662ed20065
commit 666271c105
2 changed files with 24 additions and 10 deletions
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17
src/math/scalbn.c
View File

@ -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;
}

17
src/math/scalbnf.c
View File

@ -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;
}