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MPILIB: Provide count_leading/trailing_zeros() based on arch functions
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Provide count_leading/trailing_zeros() macros based on extant arch bit scanning
functions rather than reimplementing from scratch in MPILIB.

Whilst we're at it, turn count_foo_zeros(n, x) into n = count_foo_zeros(x).

Also move the definition to asm-generic as other people may be interested in
using it.

Signed-off-by: David Howells <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Dmitry Kasatkin <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
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@dhowells @rustyrussell
dhowells authored and rustyrussell committed Oct 8, 2012
1 parent cf7f601 commit aacf29b
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Showing 4 changed files with 62 additions and 139 deletions.
57 changes: 57 additions & 0 deletions include/asm-generic/bitops/count_zeros.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,57 @@
/* Count leading and trailing zeros functions
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/

#ifndef _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_
#define _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_

#include <asm/bitops.h>

/**
* count_leading_zeros - Count the number of zeros from the MSB back
* @x: The value
*
* Count the number of leading zeros from the MSB going towards the LSB in @x.
*
* If the MSB of @x is set, the result is 0.
* If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
* If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
*/
static inline int count_leading_zeros(unsigned long x)
{
if (sizeof(x) == 4)
return BITS_PER_LONG - fls(x);
else
return BITS_PER_LONG - fls64(x);
}

#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG

/**
* count_trailing_zeros - Count the number of zeros from the LSB forwards
* @x: The value
*
* Count the number of trailing zeros from the LSB going towards the MSB in @x.
*
* If the LSB of @x is set, the result is 0.
* If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
* If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
*/
static inline int count_trailing_zeros(unsigned long x)
{
#define COUNT_TRAILING_ZEROS_0 (-1)

if (sizeof(x) == 4)
return ffs(x);
else
return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
}

#endif /* _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_ */
138 changes: 2 additions & 136 deletions lib/mpi/longlong.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA. */

#include <asm-generic/bitops/count_zeros.h>

/* You have to define the following before including this file:
*
* UWtype -- An unsigned type, default type for operations (typically a "word")
Expand Down Expand Up @@ -146,12 +148,6 @@ do { \
: "1" ((USItype)(n1)), \
"r" ((USItype)(n0)), \
"r" ((USItype)(d)))

#define count_leading_zeros(count, x) \
__asm__ ("clz %0,%1" \
: "=r" ((USItype)(count)) \
: "r" ((USItype)(x)))
#define COUNT_LEADING_ZEROS_0 32
#endif /* __a29k__ */

#if defined(__alpha) && W_TYPE_SIZE == 64
Expand Down Expand Up @@ -298,11 +294,6 @@ extern UDItype __udiv_qrnnd();
: "1" ((USItype)(nh)), \
"0" ((USItype)(nl)), \
"g" ((USItype)(d)))
#define count_leading_zeros(count, x) \
__asm__ ("bsch/1 %1,%0" \
: "=g" (count) \
: "g" ((USItype)(x)), \
"0" ((USItype)0))
#endif

/***************************************
Expand Down Expand Up @@ -354,27 +345,6 @@ do { USItype __r; \
} while (0)
extern USItype __udiv_qrnnd();
#endif /* LONGLONG_STANDALONE */
#define count_leading_zeros(count, x) \
do { \
USItype __tmp; \
__asm__ ( \
"ldi 1,%0\n" \
"extru,= %1,15,16,%%r0 ; Bits 31..16 zero?\n" \
"extru,tr %1,15,16,%1 ; No. Shift down, skip add.\n" \
"ldo 16(%0),%0 ; Yes. Perform add.\n" \
"extru,= %1,23,8,%%r0 ; Bits 15..8 zero?\n" \
"extru,tr %1,23,8,%1 ; No. Shift down, skip add.\n" \
"ldo 8(%0),%0 ; Yes. Perform add.\n" \
"extru,= %1,27,4,%%r0 ; Bits 7..4 zero?\n" \
"extru,tr %1,27,4,%1 ; No. Shift down, skip add.\n" \
"ldo 4(%0),%0 ; Yes. Perform add.\n" \
"extru,= %1,29,2,%%r0 ; Bits 3..2 zero?\n" \
"extru,tr %1,29,2,%1 ; No. Shift down, skip add.\n" \
"ldo 2(%0),%0 ; Yes. Perform add.\n" \
"extru %1,30,1,%1 ; Extract bit 1.\n" \
"sub %0,%1,%0 ; Subtract it. " \
: "=r" (count), "=r" (__tmp) : "1" (x)); \
} while (0)
#endif /* hppa */

/***************************************
Expand Down Expand Up @@ -457,15 +427,6 @@ do { \
: "0" ((USItype)(n0)), \
"1" ((USItype)(n1)), \
"rm" ((USItype)(d)))
#define count_leading_zeros(count, x) \
do { \
USItype __cbtmp; \
__asm__ ("bsrl %1,%0" \
: "=r" (__cbtmp) : "rm" ((USItype)(x))); \
(count) = __cbtmp ^ 31; \
} while (0)
#define count_trailing_zeros(count, x) \
__asm__ ("bsfl %1,%0" : "=r" (count) : "rm" ((USItype)(x)))
#ifndef UMUL_TIME
#define UMUL_TIME 40
#endif
Expand Down Expand Up @@ -536,15 +497,6 @@ do { \
"dI" ((USItype)(d))); \
(r) = __rq.__i.__l; (q) = __rq.__i.__h; \
} while (0)
#define count_leading_zeros(count, x) \
do { \
USItype __cbtmp; \
__asm__ ("scanbit %1,%0" \
: "=r" (__cbtmp) \
: "r" ((USItype)(x))); \
(count) = __cbtmp ^ 31; \
} while (0)
#define COUNT_LEADING_ZEROS_0 (-32) /* sic */
#if defined(__i960mx) /* what is the proper symbol to test??? */
#define rshift_rhlc(r, h, l, c) \
do { \
Expand Down Expand Up @@ -603,11 +555,6 @@ do { \
: "0" ((USItype)(n0)), \
"1" ((USItype)(n1)), \
"dmi" ((USItype)(d)))
#define count_leading_zeros(count, x) \
__asm__ ("bfffo %1{%b2:%b2},%0" \
: "=d" ((USItype)(count)) \
: "od" ((USItype)(x)), "n" (0))
#define COUNT_LEADING_ZEROS_0 32
#else /* not mc68020 */
#define umul_ppmm(xh, xl, a, b) \
do { USItype __umul_tmp1, __umul_tmp2; \
Expand Down Expand Up @@ -664,15 +611,6 @@ do { USItype __umul_tmp1, __umul_tmp2; \
"rJ" ((USItype)(bh)), \
"rJ" ((USItype)(al)), \
"rJ" ((USItype)(bl)))
#define count_leading_zeros(count, x) \
do { \
USItype __cbtmp; \
__asm__ ("ff1 %0,%1" \
: "=r" (__cbtmp) \
: "r" ((USItype)(x))); \
(count) = __cbtmp ^ 31; \
} while (0)
#define COUNT_LEADING_ZEROS_0 63 /* sic */
#if defined(__m88110__)
#define umul_ppmm(wh, wl, u, v) \
do { \
Expand Down Expand Up @@ -779,12 +717,6 @@ do { \
: "0" (__xx.__ll), \
"g" ((USItype)(d))); \
(r) = __xx.__i.__l; (q) = __xx.__i.__h; })
#define count_trailing_zeros(count, x) \
do { \
__asm__("ffsd %2,%0" \
: "=r"((USItype) (count)) \
: "0"((USItype) 0), "r"((USItype) (x))); \
} while (0)
#endif /* __ns32000__ */

/***************************************
Expand Down Expand Up @@ -855,11 +787,6 @@ do { \
"rI" ((USItype)(al)), \
"r" ((USItype)(bl))); \
} while (0)
#define count_leading_zeros(count, x) \
__asm__ ("{cntlz|cntlzw} %0,%1" \
: "=r" ((USItype)(count)) \
: "r" ((USItype)(x)))
#define COUNT_LEADING_ZEROS_0 32
#if defined(_ARCH_PPC)
#define umul_ppmm(ph, pl, m0, m1) \
do { \
Expand Down Expand Up @@ -1001,19 +928,6 @@ do { \
} while (0)
#define UMUL_TIME 20
#define UDIV_TIME 200
#define count_leading_zeros(count, x) \
do { \
if ((x) >= 0x10000) \
__asm__ ("clz %0,%1" \
: "=r" ((USItype)(count)) \
: "r" ((USItype)(x) >> 16)); \
else { \
__asm__ ("clz %0,%1" \
: "=r" ((USItype)(count)) \
: "r" ((USItype)(x))); \
(count) += 16; \
} \
} while (0)
#endif /* RT/ROMP */

/***************************************
Expand Down Expand Up @@ -1142,13 +1056,6 @@ do { \
"rI" ((USItype)(d)) \
: "%g1" __AND_CLOBBER_CC)
#define UDIV_TIME 37
#define count_leading_zeros(count, x) \
__asm__ ("scan %1,0,%0" \
: "=r" ((USItype)(x)) \
: "r" ((USItype)(count)))
/* Early sparclites return 63 for an argument of 0, but they warn that future
implementations might change this. Therefore, leave COUNT_LEADING_ZEROS_0
undefined. */
#endif /* __sparclite__ */
#endif /* __sparc_v8__ */
/* Default to sparc v7 versions of umul_ppmm and udiv_qrnnd. */
Expand Down Expand Up @@ -1454,47 +1361,6 @@ do { \
#define udiv_qrnnd __udiv_qrnnd_c
#endif

#undef count_leading_zeros
#if !defined(count_leading_zeros)
extern
#ifdef __STDC__
const
#endif
unsigned char __clz_tab[];
#define count_leading_zeros(count, x) \
do { \
UWtype __xr = (x); \
UWtype __a; \
\
if (W_TYPE_SIZE <= 32) { \
__a = __xr < ((UWtype) 1 << 2*__BITS4) \
? (__xr < ((UWtype) 1 << __BITS4) ? 0 : __BITS4) \
: (__xr < ((UWtype) 1 << 3*__BITS4) ? 2*__BITS4 : 3*__BITS4); \
} \
else { \
for (__a = W_TYPE_SIZE - 8; __a > 0; __a -= 8) \
if (((__xr >> __a) & 0xff) != 0) \
break; \
} \
\
(count) = W_TYPE_SIZE - (__clz_tab[__xr >> __a] + __a); \
} while (0)
/* This version gives a well-defined value for zero. */
#define COUNT_LEADING_ZEROS_0 W_TYPE_SIZE
#endif

#if !defined(count_trailing_zeros)
/* Define count_trailing_zeros using count_leading_zeros. The latter might be
defined in asm, but if it is not, the C version above is good enough. */
#define count_trailing_zeros(count, x) \
do { \
UWtype __ctz_x = (x); \
UWtype __ctz_c; \
count_leading_zeros(__ctz_c, __ctz_x & -__ctz_x); \
(count) = W_TYPE_SIZE - 1 - __ctz_c; \
} while (0)
#endif

#ifndef UDIV_NEEDS_NORMALIZATION
#define UDIV_NEEDS_NORMALIZATION 0
#endif
2 changes: 1 addition & 1 deletion lib/mpi/mpi-bit.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ unsigned mpi_get_nbits(MPI a)
if (a->nlimbs) {
mpi_limb_t alimb = a->d[a->nlimbs - 1];
if (alimb)
count_leading_zeros(n, alimb);
n = count_leading_zeros(alimb);
else
n = BITS_PER_MPI_LIMB;
n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
Expand Down
4 changes: 2 additions & 2 deletions lib/mpi/mpi-pow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
mp = mp_marker = mpi_alloc_limb_space(msize);
if (!mp)
goto enomem;
count_leading_zeros(mod_shift_cnt, mod->d[msize - 1]);
mod_shift_cnt = count_leading_zeros(mod->d[msize - 1]);
if (mod_shift_cnt)
mpihelp_lshift(mp, mod->d, msize, mod_shift_cnt);
else
Expand Down Expand Up @@ -169,7 +169,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)

i = esize - 1;
e = ep[i];
count_leading_zeros(c, e);
c = count_leading_zeros(e);
e = (e << c) << 1; /* shift the exp bits to the left, lose msb */
c = BITS_PER_MPI_LIMB - 1 - c;

Expand Down

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