zerobytes.c

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/* @(#)zerobytes.c  1.2 11/07/30 Copyright Copyright 1987, 1995-2011 J. Schilling */
/*
 *  fill memory with null bytes
 *
 *  Copyright (c) 1987, 1995-2011 J. Schilling
 */
/*
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * See the file CDDL.Schily.txt in this distribution for details.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file CDDL.Schily.txt from this distribution.
 */
 
#include <schily/standard.h>
#include <schily/align.h>
#include <schily/types.h>
#include <schily/schily.h>
 
#define DO8(a)  a; a; a; a; a; a; a; a;
 
/*
 * zero(to, cnt)
 */
EXPORT char *
zerobytes(tov, cnt)
    void    *tov;
    ssize_t cnt;
{
    register char   *to = (char *)tov;
    register ssize_t n;
    register long   lval = 0L;
 
    /*
     * If we change cnt to be unsigned, check for == instead of <=
     */
    if ((n = cnt) <= 0)
        return (to);
 
    if (n < 8 * sizeof (long)) {    /* Simple may be faster... */
        do {            /* n is always > 0 */
            *to++ = '\0';
        } while (--n > 0);
        return (to);
    }
 
    /*
     * Assign byte-wise until properly aligned for a long pointer.
     */
    while (--n >= 0 && !laligned(to)) {
        *to++ = '\0';
    }
    n++;
 
    if (n >= (ssize_t)(8 * sizeof (long))) {
        register ssize_t rem = n % (8 * sizeof (long));
 
        n /= (8 * sizeof (long));
        {
            register long *tol = (long *)to;
 
            do {
                DO8 (*tol++ = lval);
            } while (--n > 0);
 
            to = (char *)tol;
        }
        n = rem;
 
        if (n >= 8) {
            n -= 8;
            do {
                DO8 (*to++ = '\0');
            } while ((n -= 8) >= 0);
            n += 8;
        }
        if (n > 0) do {
            *to++ = '\0';
        } while (--n > 0);
        return (to);
    }
    if (n > 0) do {
        *to++ = '\0';
    } while (--n > 0);
    return (to);
}