/*++

Copyright (c) 1996  Microsoft Corporation

Module Name:

    util.c

Abstract:

    This file contains utilitarian functions for
    the FAX TIFF library.

Environment:

        WIN32 User Mode

Author:

    Wesley Witt (wesw) 17-Feb-1996

--*/

#include "tifflibp.h"
#pragma hdrstop



INT
FindWhiteRun(
    PBYTE       pbuf,
    INT         startBit,
    INT         stopBit
    )

/*++

Routine Description:

    Find the next span of white pixels on the specified line

Arguments:

    pbuf        - Points to uncompressed pixel data for the current line
    startBit    - Starting bit index
    stopBit     - Last bit index

Return Value:

    Length of the next run of white pixels

--*/

{
    static const BYTE WhiteRuns[256] = {

        8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
        3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
    };

    INT run, bits, n;

    pbuf += (startBit >> 3);
    if ((bits = stopBit-startBit) <= 0)
        return 0;

    //
    // Take care of the case where starting bit index is not a multiple of 8
    //

    if (n = (startBit & 7)) {

        run = WhiteRuns[(*pbuf << n) & 0xff];
        if (run > BYTEBITS-n)
            run = BYTEBITS-n;
        if (n+run < BYTEBITS)
            return run;
        bits -= run;
        pbuf++;

    } else
        run = 0;

    //
    // Look for consecutive DWORD value = 0
    //

    if (bits >= DWORDBITS * 2) {

        PDWORD  pdw;

        //
        // Align to a DWORD boundary first
        //

        while ((ULONG_PTR) pbuf & 3) {

            if (*pbuf != 0)
                return run + WhiteRuns[*pbuf];

            run += BYTEBITS;
            bits -= BYTEBITS;
            pbuf++;
        }

        pdw = (PDWORD) pbuf;

        while (bits >= DWORDBITS && *pdw == 0) {

            pdw++;
            run += DWORDBITS;
            bits -= DWORDBITS;
        }

        pbuf = (PBYTE) pdw;
    }

    //
    // Look for consecutive BYTE value = 0
    //

    while (bits >= BYTEBITS) {

        if (*pbuf != 0)
            return run + WhiteRuns[*pbuf];

        pbuf++;
        run += BYTEBITS;
        bits -= BYTEBITS;
    }

    //
    // Count the number of white pixels in the last byte
    //

    if (bits > 0)
        run += WhiteRuns[*pbuf];

    return run;
}


INT
FindBlackRun(
    PBYTE       pbuf,
    INT         startBit,
    INT         stopBit
    )

/*++

Routine Description:

    Find the next span of black pixels on the specified line

Arguments:

    pbuf        - Points to uncompressed pixel data for the current line
    startBit    - Starting bit index
    stopBit     - Last bit index

Return Value:

    Length of the next run of black pixels

--*/

{
    static const BYTE BlackRuns[256] = {

        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
        4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 7, 8
    };

    INT run, bits, n;

    pbuf += (startBit >> 3);
    if ((bits = stopBit-startBit) <= 0)
        return 0;

    //
    // Take care of the case where starting bit index is not a multiple of 8
    //

    if (n = (startBit & 7)) {

        run = BlackRuns[(*pbuf << n) & 0xff];
        if (run > BYTEBITS-n)
            run = BYTEBITS-n;
        if (n+run < BYTEBITS)
            return run;
        bits -= run;
        pbuf++;

    } else
        run = 0;

    //
    // Look for consecutive DWORD value = 0xffffffff
    //

    if (bits >= DWORDBITS * 2) {

        PDWORD  pdw;

        //
        // Align to a DWORD boundary first
        //

        while ((ULONG_PTR) pbuf & 3) {

            if (*pbuf != 0xff)
                return run + BlackRuns[*pbuf];

            run += BYTEBITS;
            bits -= BYTEBITS;
            pbuf++;
        }

        pdw = (PDWORD) pbuf;

        while (bits >= DWORDBITS && *pdw == 0xffffffff) {

            pdw++;
            run += DWORDBITS;
            bits -= DWORDBITS;
        }

        pbuf = (PBYTE) pdw;
    }

    //
    // Look for consecutive BYTE value = 0xff
    //

    while (bits >= BYTEBITS) {

        if (*pbuf != 0xff)
            return run + BlackRuns[*pbuf];

        pbuf++;
        run += BYTEBITS;
        bits -= BYTEBITS;
    }

    //
    // Count the number of white pixels in the last byte
    //

    if (bits > 0)
        run += BlackRuns[*pbuf];

    return run;
}