Developer CD Series 1998 November: Tool Chest/Dev.CD Nov 98 TC.toast/Sample Code/Snippets/Sound/SndPlayDoubleBuffer/_source/MungeBuffer.c

C/C++ Source or Header | 1996-11-15 | 4.6 KB | 155 lines | [TEXT/CWIE]

/*
**    Apple Macintosh Developer Technical Support
**
**    Routines demonstrating how to manipulate buffers of WAVE data to get them to play correctly.
**
**    by Mark Cookson, Apple Developer Technical Support
**
**    File:    MungeBuffer.c
**
**    Copyright ©1996 Apple Computer, Inc.
**    All rights reserved.
**
**    You may incorporate this sample code into your applications without
**    restriction, though the sample code has been provided "AS IS" and the
**    responsibility for its operation is 100% yours.  However, what you are
**    not permitted to do is to redistribute the source as "Apple Sample
**    Code" after having made changes. If you're going to re-distribute the
**    source, we require that you make it clear in the source that the code
**    was descended from Apple Sample Code, but that you've made changes.
*/

#include "MungeBuffer.h"

/* This PowerPC assembly routine is used to make a buffer of WAVE sound
   data play as if it was a buffer of a AIFF sound data.

   All this really means is that you have to do the endian conversion without
   rearanging the channels if the sound is stereo.

   The buffer addressed is passed in register r3 and the count is passed in r4.
*/
#ifdef ASM    // Should we use the assembly versions or the C versions of the buffer munging routines?

#ifdef powerc

asm void Endian16BitBuffer (Ptr buf, unsigned long count)
{
        b        test                        // Make sure count is good
more:    subi    r4, r4, 0x04                // Move pointer back 4 bytes to next long
        lwzx    r5, r3, r4                    // Load the long
        rlwinm    r5, r5, 0x10, 0x00, 0x1F    // Rotate long left 16 bits
        stwbrx    r5, r3, r4                    // Write it back out byte reversed
test:    cmpwi    r4, 0x03                    // Are we done yet?
        bgt        more                        // Go back to process more longs
        blr                                    // We're outta here
}

/* These are the coresponding 68K versions of the above PowerPC assembly buffer munging routines.

   These calls will be called if the target is a 68K based Mac.

   The buffer address is passed as the second value (from the top) of the stack, and the count
   is the third value (from the top) of the stack.
*/

#else //generating 68K

asm void Endian16BitBuffer (Ptr buf, unsigned long count)
{
        movea.l    0x04(sp), a0                // Put address of buffer in a0
        move.l    0x08(sp), d0                // Put count in d0
        lsr.l    #0x02, d0                    // Divide count by 4
        bra        test                        // Make sure count is good
more:    move.l    (a0), d1                    // Load the long
        ror.w    #0x08, d1                    // Rotate bottom 16 bits
        swap    d1                            // Swap upper and lower words of d1
        ror.w    #0x08, d1                    // Rotate bottom 16 bits (used to be top bits)
        swap    d1                            // Swap upper and lower words of d1
        move.l    d1, (a0)+                    // Store the result
test:    dbra    d0, more                    // Go back and process more longs
        rts                                    // We're outta here
}

#endif

#else

/* Use C functions instead of assembly functions.
   To use these functions, undefine ASM in MungeBuffer.h.
*/

void Endian16BitBuffer (Ptr buf, unsigned long count)
{
    unsigned long    i;
    unsigned char    tempChar;

    for (i = kStartOfBuffer; i < count; i += sizeof (short)) {
        tempChar = (buf)[i];
        (buf)[i] = (buf)[i+1];
        (buf)[i+1] = tempChar;
    }
}

#endif

void ReverseMono8BitBuffer (const Ptr buf, unsigned long count)
{
    unsigned char    *endBuffer;
    unsigned char    *startBuffer = (unsigned char *)buf;
    unsigned char    saveByte;
    long            i;

    endBuffer = ((unsigned char *)buf + count) - 1;
    for (i = (count / (sizeof (char) * kHalfOfBuffer)); i >= kStartOfBuffer; --i) {
        saveByte = *endBuffer;
        *endBuffer-- = *startBuffer;
        *startBuffer++ = saveByte;
    }
}

void ReverseStereo8BitBuffer (const Ptr buf, unsigned long count)
{
    unsigned short    *endBuffer;
    unsigned short    *startBuffer = (unsigned short *)buf;
    unsigned short    saveShort;
    long            i;

    endBuffer = (unsigned short *)(buf + count) - 1;
    for (i = (count / (sizeof (short) * kHalfOfBuffer)); i >= kStartOfBuffer; --i) {
        saveShort = *endBuffer;
        *endBuffer-- = *startBuffer;
        *startBuffer++ = saveShort;
    }
}

void ReverseMono16BitBuffer (const Ptr buf, unsigned long count)
{
    unsigned short    *endBuffer;
    unsigned short    *startBuffer = (unsigned short *)buf;
    unsigned short    saveShort;
    long            i;

    endBuffer = (unsigned short *)(buf + count) - 1;
    for (i = (count / (sizeof (short) * kHalfOfBuffer)); i >= kStartOfBuffer; --i) {
        saveShort = *endBuffer;
        *endBuffer-- = *startBuffer;
        *startBuffer++ = saveShort;
    }
}

void ReverseStereo16BitBuffer (const Ptr buf, unsigned long count)
{
    unsigned long    *endBuffer;
    unsigned long    *startBuffer = (unsigned long *)buf;
    unsigned long    saveLong;
    long            i;

    endBuffer = (unsigned long *)(buf + count) - 1;
    for (i = (count / (sizeof (long) * kHalfOfBuffer)); i >= kStartOfBuffer; --i) {
        saveLong = *endBuffer;
        *endBuffer-- = *startBuffer;
        *startBuffer++ = saveLong;
    }
}