glibc/sysdeps/generic/divmod_1.c
Roland McGrath 8f5ca04bc7 Sat Oct 14 02:52:36 1995 Ulrich Drepper <drepper@ipd.info.uni-karlsruhe.de>
* malloc/malloc.c (_malloc_internal): Performance fix.  Move
	if statement out of loop.

	* stdio/_itoa.c, stdio/_itoa.h: Complete rewrite.  Much faster
	implementation using GMP functions.  Contributed by
	Torbjorn Granlund and Ulrich Drepper.

	* stdio/test_rdwr.c: Include <errno.h>.

	* sysdeps/i386/i586/Implies: New file.

	New highly optimized string functions for i[345]86.
	* sysdeps/i386/memchr.S, sysdeps/i386/memcmp.S: New files.
        * sysdeps/i386/stpcpy.S, sysdeps/i386/stpncpy.S: New files.
        * sysdeps/i386/strchr.S, sysdeps/i386/strcspn.S: New files.
        * sysdeps/i386/strpbrk.S, sysdeps/i386/strrchr.S: New files.
        * sysdeps/i386/strspn.S, sysdeps/i386/i486/strcat.S: New files.
        * sysdeps/i386/i486/strlen.S, sysdeps/i386/i586/strchr.S: New files.
        * sysdeps/i386/i586/strlen.S: New file.
	* sysdeps/i386/memchr.c: Removed.  There is now an assembler version.

	* sysdeps/i386/i586/memcopy.h (WORD_COPY_BWD): Parameters did
	not correspond to used values.

	* sysdeps/unix/sysv/linux/nfs/nfs.h: New file.  Simply a wrapper
        around a kernel header file.
	* sysdeps/unix/sysv/linux/Dist: Add it.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir)=sunrpc] (headers):
	Likewise.

	* sysdeps/unix/sysv/linux/local_lim.h: Rewrite.  Instead of
        defining ourself we use a kernel header file.

	* sysdeps/unix/sysv/linux/i386/sysdep.h (DO_CALL): Optimize system
        call handler for i586.

	* sysdeps/unix/sysv/linux/sys/param.h: Add copyright and clean up.
Sat Oct 14 02:52:36 1995  Ulrich Drepper  <drepper@ipd.info.uni-karlsruhe.de>

	* malloc/malloc.c (_malloc_internal): Performance fix.  Move
	if statement out of loop.

	* stdio/_itoa.c, stdio/_itoa.h: Complete rewrite.  Much faster
	implementation using GMP functions.  Contributed by
	Torbjorn Granlund and Ulrich Drepper.

	* stdio/test_rdwr.c: Include <errno.h>.

	* sysdeps/i386/i586/Implies: New file.

	New highly optimized string functions for i[345]86.
	* sysdeps/i386/memchr.S, sysdeps/i386/memcmp.S: New files.
        * sysdeps/i386/stpcpy.S, sysdeps/i386/stpncpy.S: New files.
        * sysdeps/i386/strchr.S, sysdeps/i386/strcspn.S: New files.
        * sysdeps/i386/strpbrk.S, sysdeps/i386/strrchr.S: New files.
        * sysdeps/i386/strspn.S, sysdeps/i386/i486/strcat.S: New files.
        * sysdeps/i386/i486/strlen.S, sysdeps/i386/i586/strchr.S: New files.
        * sysdeps/i386/i586/strlen.S: New file.
	* sysdeps/i386/memchr.c: Removed.  There is now an assembler version.

	* sysdeps/i386/i586/memcopy.h (WORD_COPY_BWD): Parameters did
	not correspond to used values.

	* sysdeps/unix/sysv/linux/nfs/nfs.h: New file.  Simply a wrapper
        around a kernel header file.
	* sysdeps/unix/sysv/linux/Dist: Add it.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir)=sunrpc] (headers):
	Likewise.

	* sysdeps/unix/sysv/linux/local_lim.h: Rewrite.  Instead of
        defining ourself we use a kernel header file.

	* sysdeps/unix/sysv/linux/i386/sysdep.h (DO_CALL): Optimize system
        call handler for i586.

	* sysdeps/unix/sysv/linux/sys/param.h: Add copyright and clean up.
1995-10-16 01:37:51 +00:00

208 lines
5.7 KiB
C

/* __mpn_divmod_1(quot_ptr, dividend_ptr, dividend_size, divisor_limb) --
Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB.
Write DIVIDEND_SIZE limbs of quotient at QUOT_PTR.
Return the single-limb remainder.
There are no constraints on the value of the divisor.
QUOT_PTR and DIVIDEND_PTR might point to the same limb.
Copyright (C) 1991, 1993, 1994 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
The GNU MP 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#ifndef UMUL_TIME
#define UMUL_TIME 1
#endif
#ifndef UDIV_TIME
#define UDIV_TIME UMUL_TIME
#endif
/* FIXME: We should be using invert_limb (or invert_normalized_limb)
here (not udiv_qrnnd). */
mp_limb
#if __STDC__
__mpn_divmod_1 (mp_ptr quot_ptr,
mp_srcptr dividend_ptr, mp_size_t dividend_size,
mp_limb divisor_limb)
#else
__mpn_divmod_1 (quot_ptr, dividend_ptr, dividend_size, divisor_limb)
mp_ptr quot_ptr;
mp_srcptr dividend_ptr;
mp_size_t dividend_size;
mp_limb divisor_limb;
#endif
{
mp_size_t i;
mp_limb n1, n0, r;
int dummy;
/* ??? Should this be handled at all? Rely on callers? */
if (dividend_size == 0)
return 0;
/* If multiplication is much faster than division, and the
dividend is large, pre-invert the divisor, and use
only multiplications in the inner loop. */
/* This test should be read:
Does it ever help to use udiv_qrnnd_preinv?
&& Does what we save compensate for the inversion overhead? */
if (UDIV_TIME > (2 * UMUL_TIME + 6)
&& (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME)
{
int normalization_steps;
count_leading_zeros (normalization_steps, divisor_limb);
if (normalization_steps != 0)
{
mp_limb divisor_limb_inverted;
divisor_limb <<= normalization_steps;
/* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
most significant bit (with weight 2**N) implicit. */
/* Special case for DIVISOR_LIMB == 100...000. */
if (divisor_limb << 1 == 0)
divisor_limb_inverted = ~(mp_limb) 0;
else
udiv_qrnnd (divisor_limb_inverted, dummy,
-divisor_limb, 0, divisor_limb);
n1 = dividend_ptr[dividend_size - 1];
r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
/* Possible optimization:
if (r == 0
&& divisor_limb > ((n1 << normalization_steps)
| (dividend_ptr[dividend_size - 2] >> ...)))
...one division less... */
for (i = dividend_size - 2; i >= 0; i--)
{
n0 = dividend_ptr[i];
udiv_qrnnd_preinv (quot_ptr[i + 1], r, r,
((n1 << normalization_steps)
| (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
divisor_limb, divisor_limb_inverted);
n1 = n0;
}
udiv_qrnnd_preinv (quot_ptr[0], r, r,
n1 << normalization_steps,
divisor_limb, divisor_limb_inverted);
return r >> normalization_steps;
}
else
{
mp_limb divisor_limb_inverted;
/* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The
result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
most significant bit (with weight 2**N) implicit. */
/* Special case for DIVISOR_LIMB == 100...000. */
if (divisor_limb << 1 == 0)
divisor_limb_inverted = ~(mp_limb) 0;
else
udiv_qrnnd (divisor_limb_inverted, dummy,
-divisor_limb, 0, divisor_limb);
i = dividend_size - 1;
r = dividend_ptr[i];
if (r >= divisor_limb)
r = 0;
else
{
quot_ptr[i] = 0;
i--;
}
for (; i >= 0; i--)
{
n0 = dividend_ptr[i];
udiv_qrnnd_preinv (quot_ptr[i], r, r,
n0, divisor_limb, divisor_limb_inverted);
}
return r;
}
}
else
{
if (UDIV_NEEDS_NORMALIZATION)
{
int normalization_steps;
count_leading_zeros (normalization_steps, divisor_limb);
if (normalization_steps != 0)
{
divisor_limb <<= normalization_steps;
n1 = dividend_ptr[dividend_size - 1];
r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
/* Possible optimization:
if (r == 0
&& divisor_limb > ((n1 << normalization_steps)
| (dividend_ptr[dividend_size - 2] >> ...)))
...one division less... */
for (i = dividend_size - 2; i >= 0; i--)
{
n0 = dividend_ptr[i];
udiv_qrnnd (quot_ptr[i + 1], r, r,
((n1 << normalization_steps)
| (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
divisor_limb);
n1 = n0;
}
udiv_qrnnd (quot_ptr[0], r, r,
n1 << normalization_steps,
divisor_limb);
return r >> normalization_steps;
}
}
/* No normalization needed, either because udiv_qrnnd doesn't require
it, or because DIVISOR_LIMB is already normalized. */
i = dividend_size - 1;
r = dividend_ptr[i];
if (r >= divisor_limb)
r = 0;
else
{
quot_ptr[i] = 0;
i--;
}
for (; i >= 0; i--)
{
n0 = dividend_ptr[i];
udiv_qrnnd (quot_ptr[i], r, r, n0, divisor_limb);
}
return r;
}
}