memset_64.c

Go to the documentation of this file.

/*
 * Copyright 2011 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program 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, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <arch/chip.h>

#include <linux/types.h>
#include <linux/string.h>
#include <linux/module.h>

#undef memset

void *memset(void *s, int c, size_t n)
{
    uint64_t *out64;
    int n64, to_align64;
    uint64_t v64;
    uint8_t *out8 = s;

    /* Experimentation shows that a trivial tight loop is a win up until
     * around a size of 20, where writing a word at a time starts to win.
     */
#define BYTE_CUTOFF 20

#if BYTE_CUTOFF < 7
    /* This must be at least at least this big, or some code later
     * on doesn't work.
     */
#error "BYTE_CUTOFF is too small"
#endif

    if (n < BYTE_CUTOFF) {
        /* Strangely, this turns out to be the tightest way to
         * write this loop.
         */
        if (n != 0) {
            do {
                /* Strangely, combining these into one line
                 * performs worse.
                 */
                *out8 = c;
                out8++;
            } while (--n != 0);
        }

        return s;
    }

    /* Align 'out8'. We know n >= 7 so this won't write past the end. */
    while (((uintptr_t) out8 & 7) != 0) {
        *out8++ = c;
        --n;
    }

    /* Align 'n'. */
    while (n & 7)
        out8[--n] = c;

    out64 = (uint64_t *) out8;
    n64 = n >> 3;

    /* Tile input byte out to 64 bits. */
    /* KLUDGE */
    v64 = 0x0101010101010101ULL * (uint8_t)c;

    /* This must be at least 8 or the following loop doesn't work. */
#define CACHE_LINE_SIZE_IN_DOUBLEWORDS (CHIP_L2_LINE_SIZE() / 8)

    /* Determine how many words we need to emit before the 'out32'
     * pointer becomes aligned modulo the cache line size.
     */
    to_align64 = (-((uintptr_t)out64 >> 3)) &
        (CACHE_LINE_SIZE_IN_DOUBLEWORDS - 1);

    /* Only bother aligning and using wh64 if there is at least
     * one full cache line to process.  This check also prevents
     * overrunning the end of the buffer with alignment words.
     */
    if (to_align64 <= n64 - CACHE_LINE_SIZE_IN_DOUBLEWORDS) {
        int lines_left;

        /* Align out64 mod the cache line size so we can use wh64. */
        n64 -= to_align64;
        for (; to_align64 != 0; to_align64--) {
            *out64 = v64;
            out64++;
        }

        /* Use unsigned divide to turn this into a right shift. */
        lines_left = (unsigned)n64 / CACHE_LINE_SIZE_IN_DOUBLEWORDS;

        do {
            /* Only wh64 a few lines at a time, so we don't
             * exceed the maximum number of victim lines.
             */
            int x = ((lines_left < CHIP_MAX_OUTSTANDING_VICTIMS())
                  ? lines_left
                  : CHIP_MAX_OUTSTANDING_VICTIMS());
            uint64_t *wh = out64;
            int i = x;
            int j;

            lines_left -= x;

            do {
                __insn_wh64(wh);
                wh += CACHE_LINE_SIZE_IN_DOUBLEWORDS;
            } while (--i);

            for (j = x * (CACHE_LINE_SIZE_IN_DOUBLEWORDS / 4);
                 j != 0; j--) {
                *out64++ = v64;
                *out64++ = v64;
                *out64++ = v64;
                *out64++ = v64;
            }
        } while (lines_left != 0);

        /* We processed all full lines above, so only this many
         * words remain to be processed.
         */
        n64 &= CACHE_LINE_SIZE_IN_DOUBLEWORDS - 1;
    }

    /* Now handle any leftover values. */
    if (n64 != 0) {
        do {
            *out64 = v64;
            out64++;
        } while (--n64 != 0);
    }

    return s;
}
EXPORT_SYMBOL(memset);