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math: ilogb cleanup

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* consistent code style
* explicit union instead of typedef for double and float bit access
* turn FENV_ACCESS ON to make 0/0.0f raise invalid flag
* (untested) ld128 version of ilogbl (used by logbl which has ld128 support)
This commit is contained in:
Szabolcs Nagy 2013-09-02 23:33:20 +00:00
parent af5f6d9556
commit 4cec31fc23
3 changed files with 43 additions and 16 deletions
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14
src/math/ilogb.c
View File

@ -3,22 +3,24 @@
int ilogb(double x) int ilogb(double x)
{ {
union dshape u = {x}; #pragma STDC FENV_ACCESS ON
int e = u.bits>>52 & 0x7ff; union {double f; uint64_t i;} u = {x};
uint64_t i = u.i;
int e = i>>52 & 0x7ff;
if (!e) { if (!e) {
u.bits <<= 12; i <<= 12;
if (u.bits == 0) { if (i == 0) {
FORCE_EVAL(0/0.0f); FORCE_EVAL(0/0.0f);
return FP_ILOGB0; return FP_ILOGB0;
} }
/* subnormal x */ /* subnormal x */
for (e = -0x3ff; u.bits < (uint64_t)1<<63; e--, u.bits<<=1); for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
return e; return e;
} }
if (e == 0x7ff) { if (e == 0x7ff) {
FORCE_EVAL(0/0.0f); FORCE_EVAL(0/0.0f);
return u.bits<<12 ? FP_ILOGBNAN : INT_MAX; return i<<12 ? FP_ILOGBNAN : INT_MAX;
} }
return e - 0x3ff; return e - 0x3ff;
} }

14
src/math/ilogbf.c
View File

@ -3,22 +3,24 @@
int ilogbf(float x) int ilogbf(float x)
{ {
union fshape u = {x}; #pragma STDC FENV_ACCESS ON
int e = u.bits>>23 & 0xff; union {float f; uint32_t i;} u = {x};
uint32_t i = u.i;
int e = i>>23 & 0xff;
if (!e) { if (!e) {
u.bits <<= 9; i <<= 9;
if (u.bits == 0) { if (i == 0) {
FORCE_EVAL(0/0.0f); FORCE_EVAL(0/0.0f);
return FP_ILOGB0; return FP_ILOGB0;
} }
/* subnormal x */ /* subnormal x */
for (e = -0x7f; u.bits < (uint32_t)1<<31; e--, u.bits<<=1); for (e = -0x7f; i>>31 == 0; e--, i<<=1);
return e; return e;
} }
if (e == 0xff) { if (e == 0xff) {
FORCE_EVAL(0/0.0f); FORCE_EVAL(0/0.0f);
return u.bits<<9 ? FP_ILOGBNAN : INT_MAX; return i<<9 ? FP_ILOGBNAN : INT_MAX;
} }
return e - 0x7f; return e - 0x7f;
} }

31
src/math/ilogbl.c
View File

@ -9,23 +9,46 @@ int ilogbl(long double x)
#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 #elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
int ilogbl(long double x) int ilogbl(long double x)
{ {
#pragma STDC FENV_ACCESS ON
union ldshape u = {x}; union ldshape u = {x};
uint64_t m = u.i.m; uint64_t m = u.i.m;
int e = u.i.se & 0x7fff; int e = u.i.se & 0x7fff;
if (!e) { if (!e) {
if (m == 0) { if (m == 0) {
FORCE_EVAL(x/x); FORCE_EVAL(0/0.0f);
return FP_ILOGB0; return FP_ILOGB0;
} }
/* subnormal x */ /* subnormal x */
for (e = -0x3fff+1; m < (uint64_t)1<<63; e--, m<<=1); for (e = -0x3fff+1; m>>63 == 0; e--, m<<=1);
return e; return e;
} }
if (e == 0x7fff) { if (e == 0x7fff) {
FORCE_EVAL(0/0.0f); FORCE_EVAL(0/0.0f);
/* in ld80 msb is set in inf */ return m<<1 ? FP_ILOGBNAN : INT_MAX;
return m << 1 ? FP_ILOGBNAN : INT_MAX; }
return e - 0x3fff;
}
#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
int ilogbl(long double x)
{
#pragma STDC FENV_ACCESS ON
union ldshape u = {x};
int e = u.i.se & 0x7fff;
if (!e) {
if (x == 0) {
FORCE_EVAL(0/0.0f);
return FP_ILOGB0;
}
/* subnormal x */
x *= 0x1p120;
return ilogbl(x) - 120;
}
if (e == 0x7fff) {
FORCE_EVAL(0/0.0f);
u.i.se = 0;
return u.f ? FP_ILOGBNAN : INT_MAX;
} }
return e - 0x3fff; return e - 0x3fff;
} }