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math: excess precision fix modf, modff, scalbn, scalbnf

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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)
This commit is contained in:
Szabolcs Nagy
2012-11-13 10:55:35 +01:00
parent 666271c105
commit c4359e0130
4 changed files with 18 additions and 22 deletions
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6
src/math/modf.c
View File

@ -1,5 +1,4 @@
#include <math.h> #include "libm.h"
#include <stdint.h>
double modf(double x, double *iptr) double modf(double x, double *iptr)
{ {
@ -33,5 +32,6 @@ double modf(double x, double *iptr)
} }
u.n &= ~mask; u.n &= ~mask;
*iptr = u.x; *iptr = u.x;
return x - *iptr; STRICT_ASSIGN(double, x, x - *iptr);
return x;
} }

6
src/math/modff.c
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@ -1,5 +1,4 @@
#include <math.h> #include "libm.h"
#include <stdint.h>
float modff(float x, float *iptr) float modff(float x, float *iptr)
{ {
@ -33,5 +32,6 @@ float modff(float x, float *iptr)
} }
u.n &= ~mask; u.n &= ~mask;
*iptr = u.x; *iptr = u.x;
return x - *iptr; STRICT_ASSIGN(float, x, x - *iptr);
return x;
} }

14
src/math/scalbn.c
View File

@ -2,8 +2,6 @@
double scalbn(double x, int n) double scalbn(double x, int n)
{ {
/* make sure result is stored as double on overflow or underflow */
volatile double z;
double scale; double scale;
if (n > 1023) { if (n > 1023) {
@ -13,8 +11,8 @@ double scalbn(double x, int n)
x *= 0x1p1023; x *= 0x1p1023;
n -= 1023; n -= 1023;
if (n > 1023) { if (n > 1023) {
z = x * 0x1p1023; STRICT_ASSIGN(double, x, x * 0x1p1023);
return z; return x;
} }
} }
} else if (n < -1022) { } else if (n < -1022) {
@ -24,12 +22,12 @@ double scalbn(double x, int n)
x *= 0x1p-1022; x *= 0x1p-1022;
n += 1022; n += 1022;
if (n < -1022) { if (n < -1022) {
z = x * 0x1p-1022; STRICT_ASSIGN(double, x, x * 0x1p-1022);
return z; return x;
} }
} }
} }
INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0); INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
z = x * scale; STRICT_ASSIGN(double, x, x * scale);
return z; return x;
} }

14
src/math/scalbnf.c
View File

@ -2,8 +2,6 @@
float scalbnf(float x, int n) float scalbnf(float x, int n)
{ {
/* make sure result is stored as double on overflow or underflow */
volatile float z;
float scale; float scale;
if (n > 127) { if (n > 127) {
@ -13,8 +11,8 @@ float scalbnf(float x, int n)
x *= 0x1p127f; x *= 0x1p127f;
n -= 127; n -= 127;
if (n > 127) { if (n > 127) {
z = x * 0x1p127f; STRICT_ASSIGN(float, x, x * 0x1p127f);
return z; return x;
} }
} }
} else if (n < -126) { } else if (n < -126) {
@ -24,12 +22,12 @@ float scalbnf(float x, int n)
x *= 0x1p-126f; x *= 0x1p-126f;
n += 126; n += 126;
if (n < -126) { if (n < -126) {
z = x * 0x1p-126f; STRICT_ASSIGN(float, x, x * 0x1p-126f);
return z; return x;
} }
} }
} }
SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23); SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23);
z = x * scale; STRICT_ASSIGN(float, x, x * scale);
return z; return x;
} }