The R Project SVN R

/*
 * Speed-optimized CRC32 using slicing-by-eight algorithm
 *
 * This uses only i386 instructions, but it is optimized for i686 and later
 * (including e.g. Pentium II/III/IV, Athlon XP, and Core 2). For i586
 * (e.g. Pentium), slicing-by-four would be better, and even the C version
 * of slicing-by-eight built with gcc -march=i586 tends to be a little bit
 * better than this. Very few probably run this code on i586 or older x86
 * so this shouldn't be a problem in practice.
 *
 * Authors: Igor Pavlov (original version)
 *          Lasse Collin (AT&T syntax, PIC support, better portability)
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 *
 * This code needs lzma_crc32_table, which can be created using the
 * following C code:

uint32_t lzma_crc32_table[8][256];

void
init_table(void)
{
    // IEEE-802.3
    static const uint32_t poly32 = UINT32_C(0xEDB88320);

    // Castagnoli
    // static const uint32_t poly32 = UINT32_C(0x82F63B78);

    // Koopman
    // static const uint32_t poly32 = UINT32_C(0xEB31D82E);

    for (size_t s = 0; s < 8; ++s) {
        for (size_t b = 0; b < 256; ++b) {
            uint32_t r = s == 0 ? b : lzma_crc32_table[s - 1][b];

            for (size_t i = 0; i < 8; ++i) {
                if (r & 1)
                    r = (r >> 1) ^ poly32;
                else
                    r >>= 1;
            }

            lzma_crc32_table[s][b] = r;
        }
    }
}

 * The prototype of the CRC32 function:
 * extern uint32_t lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc);
 */

/*
 * On some systems, the functions need to be prefixed. The prefix is
 * usually an underscore.
 */
#ifndef __USER_LABEL_PREFIX__
#   define __USER_LABEL_PREFIX__
#endif
#define MAKE_SYM_CAT(prefix, sym) prefix ## sym
#define MAKE_SYM(prefix, sym) MAKE_SYM_CAT(prefix, sym)
#define LZMA_CRC32 MAKE_SYM(__USER_LABEL_PREFIX__, lzma_crc32)
#define LZMA_CRC32_TABLE MAKE_SYM(__USER_LABEL_PREFIX__, lzma_crc32_table)

/*
 * Solaris assembler doesn't have .p2align, and Darwin uses .align
 * differently than GNU/Linux and Solaris.
 */
#if defined(__MACH__) || defined(__MSDOS__)
#   define ALIGN(pow2, abs) .align pow2
#else
#   define ALIGN(pow2, abs) .align abs
#endif

    .text
    .globl  LZMA_CRC32

#if !defined(__MACH__) && !defined(_WIN32) && !defined(__CYGWIN__) \
        && !defined(__MSDOS__)
    .type   LZMA_CRC32, @function
#endif

    ALIGN(4, 16)
LZMA_CRC32:
    /*
     * Register usage:
     * %eax crc
     * %esi buf
     * %edi size or buf + size
     * %ebx lzma_crc32_table
     * %ebp Table index
     * %ecx Temporary
     * %edx Temporary
     */
    pushl   %ebx
    pushl   %esi
    pushl   %edi
    pushl   %ebp
    movl    0x14(%esp), %esi /* buf */
    movl    0x18(%esp), %edi /* size */
    movl    0x1C(%esp), %eax /* crc */

    /*
     * Store the address of lzma_crc32_table to %ebx. This is needed to
     * get position-independent code (PIC).
     *
     * The PIC macro is defined by libtool, while __PIC__ is defined
     * by GCC but only on some systems. Testing for both makes it simpler
     * to test this code without libtool, and keeps the code working also
     * when built with libtool but using something else than GCC.
     *
     * I understood that libtool may define PIC on Windows even though
     * the code in Windows DLLs is not PIC in sense that it is in ELF
     * binaries, so we need a separate check to always use the non-PIC
     * code on Windows.
     */
#if (!defined(PIC) && !defined(__PIC__)) \
        || (defined(_WIN32) || defined(__CYGWIN__))
    /* Not PIC */
    movl    $LZMA_CRC32_TABLE, %ebx
#elif defined(__MACH__)
    /* Mach-O */
    call    .L_get_pc
.L_pic:
    leal    .L_lzma_crc32_table$non_lazy_ptr-.L_pic(%ebx), %ebx
    movl    (%ebx), %ebx
#else
    /* ELF */
    call    .L_get_pc
    addl    $_GLOBAL_OFFSET_TABLE_, %ebx
    movl    LZMA_CRC32_TABLE@GOT(%ebx), %ebx
#endif

    /* Complement the initial value. */
    notl    %eax

    ALIGN(4, 16)
.L_align:
    /*
     * Check if there is enough input to use slicing-by-eight.
     * We need 16 bytes, because the loop pre-reads eight bytes.
     */
    cmpl    $16, %edi
    jl  .L_rest

    /* Check if we have reached alignment of eight bytes. */
    testl   $7, %esi
    jz  .L_slice

    /* Calculate CRC of the next input byte. */
    movzbl  (%esi), %ebp
    incl    %esi
    movzbl  %al, %ecx
    xorl    %ecx, %ebp
    shrl    $8, %eax
    xorl    (%ebx, %ebp, 4), %eax
    decl    %edi
    jmp .L_align

    ALIGN(2, 4)
.L_slice:
    /*
     * If we get here, there's at least 16 bytes of aligned input
     * available. Make %edi multiple of eight bytes. Store the possible
     * remainder over the "size" variable in the argument stack.
     */
    movl    %edi, 0x18(%esp)
    andl    $-8, %edi
    subl    %edi, 0x18(%esp)

    /*
     * Let %edi be buf + size - 8 while running the main loop. This way
     * we can compare for equality to determine when exit the loop.
     */
    addl    %esi, %edi
    subl    $8, %edi

    /* Read in the first eight aligned bytes. */
    xorl    (%esi), %eax
    movl    4(%esi), %ecx
    movzbl  %cl, %ebp

.L_loop:
    movl    0x0C00(%ebx, %ebp, 4), %edx
    movzbl  %ch, %ebp
    xorl    0x0800(%ebx, %ebp, 4), %edx
    shrl    $16, %ecx
    xorl    8(%esi), %edx
    movzbl  %cl, %ebp
    xorl    0x0400(%ebx, %ebp, 4), %edx
    movzbl  %ch, %ebp
    xorl    (%ebx, %ebp, 4), %edx
    movzbl  %al, %ebp

    /*
     * Read the next four bytes, for which the CRC is calculated
     * on the next interation of the loop.
     */
    movl    12(%esi), %ecx

    xorl    0x1C00(%ebx, %ebp, 4), %edx
    movzbl  %ah, %ebp
    shrl    $16, %eax
    xorl    0x1800(%ebx, %ebp, 4), %edx
    movzbl  %ah, %ebp
    movzbl  %al, %eax
    movl    0x1400(%ebx, %eax, 4), %eax
    addl    $8, %esi
    xorl    %edx, %eax
    xorl    0x1000(%ebx, %ebp, 4), %eax

    /* Check for end of aligned input. */
    cmpl    %edi, %esi
    movzbl  %cl, %ebp
    jne .L_loop

    /*
     * Process the remaining eight bytes, which we have already
     * copied to %ecx and %edx.
     */
    movl    0x0C00(%ebx, %ebp, 4), %edx
    movzbl  %ch, %ebp
    xorl    0x0800(%ebx, %ebp, 4), %edx
    shrl    $16, %ecx
    movzbl  %cl, %ebp
    xorl    0x0400(%ebx, %ebp, 4), %edx
    movzbl  %ch, %ebp
    xorl    (%ebx, %ebp, 4), %edx
    movzbl  %al, %ebp

    xorl    0x1C00(%ebx, %ebp, 4), %edx
    movzbl  %ah, %ebp
    shrl    $16, %eax
    xorl    0x1800(%ebx, %ebp, 4), %edx
    movzbl  %ah, %ebp
    movzbl  %al, %eax
    movl    0x1400(%ebx, %eax, 4), %eax
    addl    $8, %esi
    xorl    %edx, %eax
    xorl    0x1000(%ebx, %ebp, 4), %eax

    /* Copy the number of remaining bytes to %edi. */
    movl    0x18(%esp), %edi

.L_rest:
    /* Check for end of input. */
    testl   %edi, %edi
    jz  .L_return

    /* Calculate CRC of the next input byte. */
    movzbl  (%esi), %ebp
    incl    %esi
    movzbl  %al, %ecx
    xorl    %ecx, %ebp
    shrl    $8, %eax
    xorl    (%ebx, %ebp, 4), %eax
    decl    %edi
    jmp .L_rest

.L_return:
    /* Complement the final value. */
    notl    %eax

    popl    %ebp
    popl    %edi
    popl    %esi
    popl    %ebx
    ret

#if defined(PIC) || defined(__PIC__)
    ALIGN(4, 16)
.L_get_pc:
    movl    (%esp), %ebx
    ret
#endif

#if defined(__MACH__) && (defined(PIC) || defined(__PIC__))
    /* Mach-O PIC */
    .section __IMPORT,__pointers,non_lazy_symbol_pointers
.L_lzma_crc32_table$non_lazy_ptr:
    .indirect_symbol LZMA_CRC32_TABLE
    .long 0

#elif defined(_WIN32) || defined(__CYGWIN__)
#   ifdef DLL_EXPORT
    /* This is equivalent of __declspec(dllexport). */
    .section .drectve
    .ascii " -export:lzma_crc32"
#   endif

#elif !defined(__MSDOS__)
    /* ELF */
    .size   LZMA_CRC32, .-LZMA_CRC32
#endif

/*
 * This is needed to support non-executable stack. It's ugly to
 * use __linux__ here, but I don't know a way to detect when
 * we are using GNU assembler.
 */
#if defined(__ELF__) && defined(__linux__)
    .section    .note.GNU-stack,"",@progbits
#endif