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math: fix acoshf on negative values 

acosh(x) is invalid for x<1, acoshf tried to be clever using
signed comparisions to handle all x<2 the same way, but the
formula was wrong on large negative values.
This commit is contained in:
Szabolcs Nagy 2013-09-05 12:26:26 +00:00
parent 0234394621
commit 101e601285
2 changed files with 8 additions and 7 deletions
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11
src/math/acoshf.c
View File

@ -3,14 +3,15 @@
/* acosh(x) = log(x + sqrt(x*x-1)) */
float acoshf(float x)
{
union {float f; int32_t i;} u = {.f = x};
union {float f; uint32_t i;} u = {x};
uint32_t a = u.i & 0x7fffffff;
if (u.i < 0x3f800000+(1<<23))
/* x < 2, invalid if x < 1 or nan */
if (a < 0x3f800000+(1<<23))
/* |x| < 2, invalid if x < 1 or nan */
/* up to 2ulp error in [1,1.125] */
return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1)));
if (u.i < 0x3f800000+(12<<23))
/* x < 0x1p12 */
if (a < 0x3f800000+(12<<23))
/* |x| < 0x1p12 */
return logf(2*x - 1/(x+sqrtf(x*x-1)));
/* x >= 0x1p12 */
return logf(x) + 0.693147180559945309417232121458176568f;

4
src/math/acoshl.c
View File

@ -13,10 +13,10 @@ long double acoshl(long double x)
int e = u.i.se & 0x7fff;
if (e < 0x3fff + 1)
/* x < 2, invalid if x < 1 or nan */
/* |x| < 2, invalid if x < 1 or nan */
return log1pl(x-1 + sqrtl((x-1)*(x-1)+2*(x-1)));
if (e < 0x3fff + 32)
/* x < 0x1p32 */
/* |x| < 0x1p32 */
return logl(2*x - 1/(x+sqrtl(x*x-1)));
return logl(x) + 0.693147180559945309417232121458176568L;
}