LXR linux/arch/tile/lib/memset

   1/*
   2 * Copyright 2011 Tilera Corporation. All Rights Reserved.
   3 *
   4 *   This program is free software; you can redistribute it and/or
   5 *   modify it under the terms of the GNU General Public License
   6 *   as published by the Free Software Foundation, version 2.
   7 *
   8 *   This program is distributed in the hope that it will be useful, but
   9 *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11 *   NON INFRINGEMENT.  See the GNU General Public License for
  12 *   more details.
  13 */
  14
  15#include <linux/types.h>
  16#include <linux/string.h>
  17#include <linux/module.h>
  18#include <arch/chip.h>
  19#include "string-endian.h"
  20
  21void *memset(void *s, int c, size_t n)
  22{
  23        uint64_t *out64;
  24        int n64, to_align64;
  25        uint64_t v64;
  26        uint8_t *out8 = s;
  27
  28        /* Experimentation shows that a trivial tight loop is a win up until
  29         * around a size of 20, where writing a word at a time starts to win.
  30         */
  31#define BYTE_CUTOFF 20
  32
  33#if BYTE_CUTOFF < 7
  34        /* This must be at least at least this big, or some code later
  35         * on doesn't work.
  36         */
  37#error "BYTE_CUTOFF is too small"
  38#endif
  39
  40        if (n < BYTE_CUTOFF) {
  41                /* Strangely, this turns out to be the tightest way to
  42                 * write this loop.
  43                 */
  44                if (n != 0) {
  45                        do {
  46                                /* Strangely, combining these into one line
  47                                 * performs worse.
  48                                 */
  49                                *out8 = c;
  50                                out8++;
  51                        } while (--n != 0);
  52                }
  53
  54                return s;
  55        }
  56
  57        /* Align 'out8'. We know n >= 7 so this won't write past the end. */
  58        while (((uintptr_t) out8 & 7) != 0) {
  59                *out8++ = c;
  60                --n;
  61        }
  62
  63        /* Align 'n'. */
  64        while (n & 7)
  65                out8[--n] = c;
  66
  67        out64 = (uint64_t *) out8;
  68        n64 = n >> 3;
  69
  70        /* Tile input byte out to 64 bits. */
  71        v64 = copy_byte(c);
  72
  73        /* This must be at least 8 or the following loop doesn't work. */
  74#define CACHE_LINE_SIZE_IN_DOUBLEWORDS (CHIP_L2_LINE_SIZE() / 8)
  75
  76        /* Determine how many words we need to emit before the 'out32'
  77         * pointer becomes aligned modulo the cache line size.
  78         */
  79        to_align64 = (-((uintptr_t)out64 >> 3)) &
  80                (CACHE_LINE_SIZE_IN_DOUBLEWORDS - 1);
  81
  82        /* Only bother aligning and using wh64 if there is at least
  83         * one full cache line to process.  This check also prevents
  84         * overrunning the end of the buffer with alignment words.
  85         */
  86        if (to_align64 <= n64 - CACHE_LINE_SIZE_IN_DOUBLEWORDS) {
  87                int lines_left;
  88
  89                /* Align out64 mod the cache line size so we can use wh64. */
  90                n64 -= to_align64;
  91                for (; to_align64 != 0; to_align64--) {
  92                        *out64 = v64;
  93                        out64++;
  94                }
  95
  96                /* Use unsigned divide to turn this into a right shift. */
  97                lines_left = (unsigned)n64 / CACHE_LINE_SIZE_IN_DOUBLEWORDS;
  98
  99                do {
 100                        /* Only wh64 a few lines at a time, so we don't
 101                         * exceed the maximum number of victim lines.
 102                         */
 103                        int x = ((lines_left < CHIP_MAX_OUTSTANDING_VICTIMS())
 104                                  ? lines_left
 105                                  : CHIP_MAX_OUTSTANDING_VICTIMS());
 106                        uint64_t *wh = out64;
 107                        int i = x;
 108                        int j;
 109
 110                        lines_left -= x;
 111
 112                        do {
 113                                __insn_wh64(wh);
 114                                wh += CACHE_LINE_SIZE_IN_DOUBLEWORDS;
 115                        } while (--i);
 116
 117                        for (j = x * (CACHE_LINE_SIZE_IN_DOUBLEWORDS / 4);
 118                             j != 0; j--) {
 119                                *out64++ = v64;
 120                                *out64++ = v64;
 121                                *out64++ = v64;
 122                                *out64++ = v64;
 123                        }
 124                } while (lines_left != 0);
 125
 126                /* We processed all full lines above, so only this many
 127                 * words remain to be processed.
 128                 */
 129                n64 &= CACHE_LINE_SIZE_IN_DOUBLEWORDS - 1;
 130        }
 131
 132        /* Now handle any leftover values. */
 133        if (n64 != 0) {
 134                do {
 135                        *out64 = v64;
 136                        out64++;
 137                } while (--n64 != 0);
 138        }
 139
 140        return s;
 141}
 142EXPORT_SYMBOL(memset);
 143