w_sqrt.s

glibc 2.9,最新版的C语言库函数

/* sqrt function.  PowerPC32 version.
   Copyright (C) 2007 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 1 Franklin Street, Fifth Floor, Boston MA
   02110-1301 USA.  */

#include <sysdep.h>
#include <math_ldbl_opt.h>

/* double [fp1] sqrt (double x [fp1])
   Power4 (ISA V2.0) and above implement sqrt in hardware (not optional).
   The fsqrt instruction generates the correct value for all inputs and
   sets the appropriate floating point exceptions.  Extented checking is
   only needed to set errno (via __kernel_standard) if the input value
   is negative.
   
   So compare the input value against the absolute value of itself.
   This will compare equal unless the value is negative (EDOM) or a NAN,
   in which case we branch to the extend wrapper.  If equal we can return
   the result directly.
   
   This part of the function looks like a leaf routine,  so no need to
   stack a frame or execute prologue/epilogue code. It is safe to
   branch directly to w_sqrt as long as the input value (f1) is
   preserved. Putting the the sqrt result into f2 (float parameter 2)
   allows passing both the input value and sqrt result into the extended
   wrapper so there is no need to recompute.
   
   This tactic avoids the overhead of stacking a frame for the normal
   (non-error) case.  Until gcc supports prologue shrink-wrapping
   this is the best we can do.  */

	.section	".text"
	.machine power4
EALIGN (__sqrt, 5, 0)
	fabs	fp0,fp1
	fsqrt	fp2,fp1
	fcmpu	cr1,fp0,fp1
	bne-	cr1,.Lw_sqrt
	fmr	fp1,fp2
	blr
	.align	4
.Lw_sqrt:
	mflr	r0
	stwu	r1,-16(r1)
	cfi_adjust_cfa_offset(16)
	fmr	fp12,fp2
	stw	r0,20(r1)
	stw	r30,8(r1)
	cfi_offset(lr,20)
	cfi_offset(r30,8)
#ifdef SHARED
# ifdef HAVE_ASM_PPC_REL16
	bcl	20,31,.LCF1
.LCF1:
	mflr	r30
	addis	r30,r30,_GLOBAL_OFFSET_TABLE_-.LCF1@ha
	addi	r30,r30,_GLOBAL_OFFSET_TABLE_-.LCF1@l
	lwz	r9,_LIB_VERSION@got(30)
	lwz	r0,0(r9)
# else
	bl	_GLOBAL_OFFSET_TABLE_@local-4
	mflr	r30
	lwz	r9,_LIB_VERSION@got(30)
	lwz	r0,0(r9)
# endif
#else
	lis	r9,_LIB_VERSION@ha
	lwz	r0,_LIB_VERSION@l(r9)
#endif
/*  if (_LIB_VERSION == _IEEE_) return z; */
	cmpwi	cr7,r0,-1
	beq-	cr7,.L4
/*  if (x != x) return z; !isnan*/
	fcmpu	cr7,fp1,fp1
	bne-	cr7,.L4
/*  if  (x < 0.0)
    return __kernel_standard (x, x, 26) */
	fmr	fp2,fp1
	li	r3,26
	bne- 	cr1,.L11
.L4:
	lwz	r0,20(r1)
	fmr	fp1,fp12
	lwz	r30,8(r1)
	addi	r1,r1,16
	mtlr 	r0
	blr
.L11:
	bl	__kernel_standard@plt
	fmr	fp12,fp1
	b	.L4
	END	(__sqrt)

weak_alias (__sqrt, sqrt)

#ifdef NO_LONG_DOUBLE
weak_alias (__sqrt, sqrtl)
strong_alias (__sqrt, __sqrtl)
#endif
#if LONG_DOUBLE_COMPAT(libm, GLIBC_2_0)
compat_symbol (libm, __sqrt, sqrtl, GLIBC_2_0)
#endif