s_ilogbl.s

来自「glibc 2.9,最新版的C语言库函数」· S 代码 · 共 36 行

/*
 * Written by J.T. Conklin <[e-mail]>.
 * Changes for long double by Ulrich Drepper <[e-mail]>
 * Adapted for x86-64 by Andreas Jaeger <[e-mail]>.
 * Public domain.
 */

#include <machine/asm.h>

ENTRY(__ilogbl)
	fldt	8(%rsp)
/* I added the following ugly construct because ilogb(+-Inf) is
   required to return INT_MAX in ISO C99.
   -- [e-mail].  */
	fxam			/* Is NaN or +-Inf?  */
	fstsw   %ax
	movb    $0x45, %dh
	andb    %ah, %dh
	cmpb    $0x05, %dh
	je      1f		/* Is +-Inf, jump.  */

	fxtract
	fstp	%st

	fistpl	-4(%rsp)
	fwait
	movl	-4(%rsp),%eax

	ret

1:	fstp	%st
	movl	$0x7fffffff, %eax
	ret
END (__ilogbl)
weak_alias (__ilogbl, ilogbl)