diff options
Diffstat (limited to 'sysdeps/i386/fpu/e_log2.S')
| -rw-r--r-- | sysdeps/i386/fpu/e_log2.S | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/sysdeps/i386/fpu/e_log2.S b/sysdeps/i386/fpu/e_log2.S new file mode 100644 index 0000000000..4f7f0d57d9 --- /dev/null +++ b/sysdeps/i386/fpu/e_log2.S @@ -0,0 +1,67 @@ +/* + * Written by J.T. Conklin <jtc@netbsd.org>. + * Adapted for use as log2 by Ulrich Drepper <drepper@cygnus.com>. + * Public domain. + * + * Changed to use fyl2xp1 for values near 1, <drepper@cygnus.com>. + */ + +#include <machine/asm.h> + +#ifdef __ELF__ + .section .rodata +#else + .text +#endif + .align ALIGNARG(4) + ASM_TYPE_DIRECTIVE(one,@object) +one: .double 1.0 + ASM_SIZE_DIRECTIVE(one) + /* It is not important that this constant is precise. It is only + a value which is known to be on the safe side for using the + fyl2xp1 instruction. */ + ASM_TYPE_DIRECTIVE(limit,@object) +limit: .double 0.29 + ASM_SIZE_DIRECTIVE(limit) + + +#ifdef PIC +#define MO(op) op##@GOTOFF(%edx) +#else +#define MO(op) op +#endif + + .text +ENTRY(__ieee754_log2) +#ifdef PIC + call 1f +1: popl %edx + addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %edx +#endif + fldl MO(one) + fldl 4(%esp) // x : 1 + fxam + fnstsw + fld %st // x : x : 1 + sahf + jc 3f // in case x is NaN or ħInf +4: fsub %st(2), %st // x-1 : x : 1 + fld %st // x-1 : x-1 : x : 1 + fabs // |x-1| : x-1 : x : 1 + fcompl MO(limit) // x-1 : x : 1 + fnstsw // x-1 : x : 1 + andb $0x45, %ah + jz 2f + fstp %st(1) // x-1 : 1 + fyl2xp1 // log(x) + ret + +2: fstp %st(0) // x : 1 + fyl2x // log(x) + ret + +3: jp 4b // in case x is ħInf + fstp %st(1) + fstp %st(1) + ret +END (__ieee754_log2) |