/*
 * Copyright (c) 2012 Alex Hornung <alex@alexhornung.com>.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <machine/asmacros.h>

        .text

/* int rdrand_rng(uint8_t *out, long limit) */
ENTRY(rdrand_rng)
        movq    %rsi,   %rcx
        shrq    $3,     %rcx    /* Divide by 8 to get 64-bit word count */

        xorq    %r11,   %r11
1:
        /*
         * rdx: (output)        entropy
         */
        rdrand  %rdx            /* rdrand64 */

        /*
         * The carry flag (CF) determines if the instruction was
         * successful or not.
         *
         * CF = 0: Random value not available at time of execution.
         */
        jae     2f

        /*
         * The operation was successful, so store the random data
         * from the register into our buffer.
         */
        movq    %rdx,   (%rdi)

        /*
         * Increment the count of stored random words as well as the
         * buffer pointer in rdi.
         */
        addq    $1,     %r11
        addq    $8,     %rdi

        /*
         * If we haven't already read enough random words,
         * loop again.
         */
        cmpq    %rcx,   %r11
        jl      1b
2:
        /* return the number of stored random bytes (random words * 8) */
        shlq    $3,     %r11
        movq    %r11,   %rax
        ret
END(rdrand_rng)