Re: [PATCH 02/25] MPILIB: Provide count_leading/trailing_zeros() based on arch functions

From: "Kasatkin, Dmitry" <dmitry.kasatkin@intel.com>
To: David Howells <dhowells@redhat.com>, James Morris <jmorris@namei.org>
Cc: rusty@rustcorp.com.au, zohar@linux.vnet.ibm.com,
	keyrings@linux-nfs.org, linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/25] MPILIB: Provide count_leading/trailing_zeros() based on arch functions
Date: Mon, 10 Sep 2012 10:13:02 +0300	[thread overview]
Message-ID: <CALLzPKbsp0EnZMTmfWtjfctsZn+YAurA_5W=hqzy1kHuxiCGng@mail.gmail.com> (raw)
In-Reply-To: <20120816013434.872.8115.stgit@warthog.procyon.org.uk>

On Thu, Aug 16, 2012 at 4:34 AM, David Howells <dhowells@redhat.com> wrote:
> 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 <dhowells@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
> Cc: Arnd Bergmann <arnd@arndb.com>

Hi James,

Can you please apply this?

Acked-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

> ---
>
>  include/asm-generic/bitops/count_zeros.h |   57 ++++++++++++
>  lib/mpi/longlong.h                       |  138 ------------------------------
>  lib/mpi/mpi-bit.c                        |    2
>  lib/mpi/mpi-pow.c                        |    4 -
>  4 files changed, 62 insertions(+), 139 deletions(-)
>  create mode 100644 include/asm-generic/bitops/count_zeros.h
>
>
> diff --git a/include/asm-generic/bitops/count_zeros.h b/include/asm-generic/bitops/count_zeros.h
> new file mode 100644
> index 0000000..97520d2
> --- /dev/null
> +++ b/include/asm-generic/bitops/count_zeros.h
> @@ -0,0 +1,57 @@
> +/* Count leading and trailing zeros functions
> + *
> + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + *
> + * 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_ */
> diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
> index 29f9862..678ce4f 100644
> --- a/lib/mpi/longlong.h
> +++ b/lib/mpi/longlong.h
> @@ -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")
> @@ -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
> @@ -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
>
>  /***************************************
> @@ -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 */
>
>  /***************************************
> @@ -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
> @@ -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 { \
> @@ -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; \
> @@ -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 { \
> @@ -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__ */
>
>  /***************************************
> @@ -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 { \
> @@ -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 */
>
>  /***************************************
> @@ -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.  */
> @@ -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
> diff --git a/lib/mpi/mpi-bit.c b/lib/mpi/mpi-bit.c
> index 5687248..503537e 100644
> --- a/lib/mpi/mpi-bit.c
> +++ b/lib/mpi/mpi-bit.c
> @@ -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;
> diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
> index 67f3e79..5464c87 100644
> --- a/lib/mpi/mpi-pow.c
> +++ b/lib/mpi/mpi-pow.c
> @@ -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
> @@ -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;
>
>