glibc/sysdeps/i386/fpu/e_acosl.c

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/*
* Written by J.T. Conklin <jtc@netbsd.org>.
* Public domain.
*
* Adapted for `long double' by Ulrich Drepper <drepper@cygnus.com>.
*/
#include <math_private.h>
long double
__ieee754_acosl (long double x)
{
long double res;
/* acosl = atanl (sqrtl(1 - x^2) / x) */
asm ( "fld %%st\n"
"fmul %%st(0)\n" /* x^2 */
"fld1\n"
"fsubp\n" /* 1 - x^2 */
"fsqrt\n" /* sqrtl (1 - x^2) */
"fxch %%st(1)\n"
"fpatan"
: "=t" (res) : "0" (x) : "st(1)");
return res;
}