--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/audio_convert.c	Mon Oct 15 20:24:28 2001 +0000
@@ -0,0 +1,731 @@
+/*
+    SDL - Simple DirectMedia Layer
+    Copyright (C) 1997, 1998, 1999, 2000, 2001  Sam Lantinga
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Library General Public
+    License as published by the Free Software Foundation; either
+    version 2 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Library General Public License for more details.
+
+    You should have received a copy of the GNU Library General Public
+    License along with this library; if not, write to the Free
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+    Sam Lantinga
+    slouken@devolution.com
+*/
+
+/*
+ * This file was derived from SDL's SDL_audiocvt.c and is an attempt to
+ * address the shortcomings of it.
+ *
+ * Perhaps we can adapt some good filters from SoX?
+ */
+
+#if HAVE_CONFIG_H
+#  include <config.h>
+#endif
+
+#include "SDL.h"
+#include "SDL_sound.h"
+
+#define __SDL_SOUND_INTERNAL__
+#include "SDL_sound_internal.h"
+
+/* Functions for audio drivers to perform runtime conversion of audio format */
+
+
+/*
+ * Toggle endianness. This filter is, of course, only applied to 16-bit
+ * audio data.
+ */
+
+void Sound_ConvertEndian(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *data, tmp;
+
+    /* SNDDBG(("Converting audio endianness\n")); */
+
+    data = cvt->buf;
+
+    for (i = cvt->len_cvt / 2; i; --i)
+    {
+        tmp = data[0];
+        data[0] = data[1];
+        data[1] = tmp;
+        data += 2;
+    } /* for */
+
+    *format = (*format ^ 0x1000);
+} /* Sound_ConvertEndian */
+
+
+/*
+ * Toggle signed/unsigned. Apparently this is done by toggling the most
+ * significant bit of each sample.
+ */
+
+void Sound_ConvertSign(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *data;
+
+    /* SNDDBG(("Converting audio signedness\n")); */
+
+    data = cvt->buf;
+
+        /* 16-bit sound? */
+    if ((*format & 0xFF) == 16)
+    {
+            /* Little-endian? */
+        if ((*format & 0x1000) != 0x1000)
+            ++data;
+
+        for (i = cvt->len_cvt / 2; i; --i)
+        {
+            *data ^= 0x80;
+            data += 2;
+        } /* for */
+    } /* if */
+    else
+    {
+        for (i = cvt->len_cvt; i; --i)
+            *data++ ^= 0x80;
+    } /* else */
+
+    *format = (*format ^ 0x8000);
+} /* Sound_ConvertSign */
+
+
+/*
+ * Convert 16-bit to 8-bit. This is done by taking the most significant byte
+ * of each 16-bit sample.
+ */
+
+void Sound_Convert8(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *src, *dst;
+
+    /* SNDDBG(("Converting to 8-bit\n")); */
+
+    src = cvt->buf;
+    dst = cvt->buf;
+
+        /* Little-endian? */
+    if ((*format & 0x1000) != 0x1000)
+        ++src;
+
+    for (i = cvt->len_cvt / 2; i; --i)
+    {
+        *dst = *src;
+        src += 2;
+        dst += 1;
+    } /* for */
+
+    *format = ((*format & ~0x9010) | AUDIO_U8);
+    cvt->len_cvt /= 2;
+} /* Sound_Convert8 */
+
+
+/* Convert 8-bit to 16-bit - LSB */
+
+void Sound_Convert16LSB(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *src, *dst;
+
+    /* SNDDBG(("Converting to 16-bit LSB\n")); */
+
+    src = cvt->buf + cvt->len_cvt;
+    dst = cvt->buf + cvt->len_cvt * 2;
+
+    for (i = cvt->len_cvt; i; --i)
+    {
+        src -= 1;
+        dst -= 2;
+        dst[1] = *src;
+        dst[0] = 0;
+    } /* for */
+
+    *format = ((*format & ~0x0008) | AUDIO_U16LSB);
+    cvt->len_cvt *= 2;
+} /* Sound_Convert16LSB */
+
+
+/* Convert 8-bit to 16-bit - MSB */
+
+void Sound_Convert16MSB(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *src, *dst;
+
+    /* SNDDBG(("Converting to 16-bit MSB\n")); */
+
+    src = cvt->buf + cvt->len_cvt;
+    dst = cvt->buf + cvt->len_cvt * 2;
+
+    for (i = cvt->len_cvt; i; --i)
+    {
+        src -= 1;
+        dst -= 2;
+        dst[0] = *src;
+        dst[1] = 0;
+    } /* for */
+
+    *format = ((*format & ~0x0008) | AUDIO_U16MSB);
+    cvt->len_cvt *= 2;
+} /* Sound_Convert16MSB */
+
+
+/* Duplicate a mono channel to both stereo channels */
+
+void Sound_ConvertStereo(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+
+    /* SNDDBG(("Converting to stereo\n")); */
+
+        /* 16-bit sound? */
+    if ((*format & 0xFF) == 16)
+    {
+        Uint16 *src, *dst;
+
+        src = (Uint16 *) (cvt->buf + cvt->len_cvt);
+        dst = (Uint16 *) (cvt->buf + cvt->len_cvt * 2);
+
+        for (i = cvt->len_cvt/2; i; --i)
+        {
+            dst -= 2;
+            src -= 1;
+            dst[0] = src[0];
+            dst[1] = src[0];
+        } /* for */
+    } /* if */
+    else
+    {
+        Uint8 *src, *dst;
+
+        src = cvt->buf + cvt->len_cvt;
+        dst = cvt->buf + cvt->len_cvt * 2;
+
+        for (i = cvt->len_cvt; i; --i)
+        {
+            dst -= 2;
+            src -= 1;
+            dst[0] = src[0];
+            dst[1] = src[0];
+        } /* for */
+    } /* else */
+
+    cvt->len_cvt *= 2;
+} /* Sound_ConvertStereo */
+
+
+/* Effectively mix right and left channels into a single channel */
+
+void Sound_ConvertMono(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Sint32 sample;
+    Uint8 *u_src, *u_dst;
+    Sint8 *s_src, *s_dst;
+
+    /* SNDDBG(("Converting to mono\n")); */
+
+    switch (*format)
+    {
+        case AUDIO_U8:
+            u_src = cvt->buf;
+            u_dst = cvt->buf;
+
+            for (i = cvt->len_cvt / 2; i; --i)
+            {
+                sample = u_src[0] + u_src[1];
+                *u_dst = (sample > 255) ? 255 : sample;
+                u_src += 2;
+                u_dst += 1;
+            } /* for */
+            break;
+
+        case AUDIO_S8:
+            s_src = (Sint8 *) cvt->buf;
+            s_dst = (Sint8 *) cvt->buf;
+
+            for (i = cvt->len_cvt / 2; i; --i)
+            {
+                sample = s_src[0] + s_src[1];
+                if (sample > 127)
+                    *s_dst = 127;
+                else if (sample < -128)
+                    *s_dst = -128;
+                else
+                    *s_dst = sample;
+
+                s_src += 2;
+                s_dst += 1;
+            } /* for */
+            break;
+
+        case AUDIO_U16MSB:
+            u_src = cvt->buf;
+            u_dst = cvt->buf;
+
+            for (i = cvt->len_cvt / 4; i; --i)
+            {
+                sample = (Uint16) ((u_src[0] << 8) | u_src[1])
+                       + (Uint16) ((u_src[2] << 8) | u_src[3]);
+                if (sample > 65535)
+                {
+                    u_dst[0] = 0xFF;
+                    u_dst[1] = 0xFF;
+                } /* if */
+                else
+                {
+                    u_dst[1] = (sample & 0xFF);
+                    sample >>= 8;
+                    u_dst[0] = (sample & 0xFF);
+                } /* else */
+                u_src += 4;
+                u_dst += 2;
+            } /* for */
+            break;
+
+        case AUDIO_U16LSB:
+            u_src = cvt->buf;
+            u_dst = cvt->buf;
+
+            for (i = cvt->len_cvt / 4; i; --i)
+            {
+                sample = (Uint16) ((u_src[1] << 8) | u_src[0])
+                       + (Uint16) ((u_src[3] << 8) | u_src[2]);
+                if (sample > 65535)
+                {
+                    u_dst[0] = 0xFF;
+                    u_dst[1] = 0xFF;
+                } /* if */
+                else
+                {
+                    u_dst[0] = (sample & 0xFF);
+                    sample >>= 8;
+                    u_dst[1] = (sample & 0xFF);
+                } /* else */
+                u_src += 4;
+                u_dst += 2;
+            } /* for */
+            break;
+
+        case AUDIO_S16MSB:
+            u_src = cvt->buf;
+            u_dst = cvt->buf;
+
+            for (i = cvt->len_cvt / 4; i; --i)
+            {
+                sample = (Sint16) ((u_src[0] << 8) | u_src[1])
+                       + (Sint16) ((u_src[2] << 8) | u_src[3]);
+                if (sample > 32767)
+                {
+                    u_dst[0] = 0x7F;
+                    u_dst[1] = 0xFF;
+                } /* if */
+                else if (sample < -32768)
+                {
+                    u_dst[0] = 0x80;
+                    u_dst[1] = 0x00;
+                } /* else if */
+                else
+                {
+                    u_dst[1] = (sample & 0xFF);
+                    sample >>= 8;
+                    u_dst[0] = (sample & 0xFF);
+                } /* else */
+                u_src += 4;
+                u_dst += 2;
+            } /* for */
+            break;
+
+        case AUDIO_S16LSB:
+            u_src = cvt->buf;
+            u_dst = cvt->buf;
+
+            for (i = cvt->len_cvt / 4; i; --i)
+            {
+                sample = (Sint16) ((u_src[1] << 8) | u_src[0])
+                       + (Sint16) ((u_src[3] << 8) | u_src[2]);
+                if (sample > 32767)
+                {
+                    u_dst[1] = 0x7F;
+                    u_dst[0] = 0xFF;
+                } /* if */
+                else if (sample < -32768)
+                {
+                    u_dst[1] = 0x80;
+                    u_dst[0] = 0x00;
+                } /* else if */
+                else
+                {
+                    u_dst[0] = (sample & 0xFF);
+                    sample >>= 8;
+                    u_dst[1] = (sample & 0xFF);
+                } /* else */
+                u_src += 4;
+                u_dst += 2;
+            } /* for */
+            break;
+    } /* switch */
+
+    cvt->len_cvt /= 2;
+} /* Sound_ConvertMono */
+
+
+/* Convert rate up by multiple of 2 */
+
+void Sound_RateMUL2(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *src, *dst;
+
+    /* SNDDBG(("Converting audio rate * 2\n")); */
+
+    src = cvt->buf + cvt->len_cvt;
+    dst = cvt->buf + cvt->len_cvt*2;
+
+        /* 8- or 16-bit sound? */
+    switch (*format & 0xFF)
+    {
+        case 8:
+            for (i = cvt->len_cvt; i; --i)
+            {
+                src -= 1;
+                dst -= 2;
+                dst[0] = src[0];
+                dst[1] = src[0];
+            } /* for */
+            break;
+
+        case 16:
+            for (i = cvt->len_cvt / 2; i; --i)
+            {
+                src -= 2;
+                dst -= 4;
+                dst[0] = src[0];
+                dst[1] = src[1];
+                dst[2] = src[0];
+                dst[3] = src[1];
+            } /* for */
+            break;
+    } /* switch */
+
+    cvt->len_cvt *= 2;
+} /* Sound_RateMUL2 */
+
+
+/* Convert rate down by multiple of 2 */
+
+void Sound_RateDIV2(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    int i;
+    Uint8 *src, *dst;
+
+    /* SNDDBG(("Converting audio rate / 2\n")); */
+
+    src = cvt->buf;
+    dst = cvt->buf;
+
+        /* 8- or 16-bit sound? */
+    switch (*format & 0xFF)
+    {
+        case 8:
+            for (i = cvt->len_cvt / 2; i; --i)
+            {
+                dst[0] = src[0];
+                src += 2;
+                dst += 1;
+            } /* for */
+            break;
+
+        case 16:
+            for (i = cvt->len_cvt / 4; i; --i)
+            {
+                dst[0] = src[0];
+                dst[1] = src[1];
+                src += 4;
+                dst += 2;
+            }
+            break;
+    } /* switch */
+
+    cvt->len_cvt /= 2;
+} /* Sound_RateDIV2 */
+
+
+/* Very slow rate conversion routine */
+
+void Sound_RateSLOW(Sound_AudioCVT *cvt, Uint16 *format)
+{
+    double ipos;
+    int i, clen;
+    Uint8 *output8;
+    Uint16 *output16;
+
+    /* SNDDBG(("Converting audio rate * %4.4f\n", 1.0/cvt->rate_incr)); */
+
+    clen = (int) ((double) cvt->len_cvt / cvt->rate_incr);
+
+    if (cvt->rate_incr > 1.0)
+    {
+            /* 8- or 16-bit sound? */
+        switch (*format & 0xFF)
+        {
+            case 8:
+                output8 = cvt->buf;
+
+                ipos = 0.0;
+                for (i = clen; i; --i)
+                {
+                    *output8 = cvt->buf[(int) ipos];
+                    ipos += cvt->rate_incr;
+                    output8 += 1;
+                } /* for */
+                break;
+
+            case 16:
+                output16 = (Uint16 *) cvt->buf;
+
+                clen &= ~1;
+                ipos = 0.0;
+                for (i = clen / 2; i; --i)
+                {
+                    *output16 = ((Uint16 *) cvt->buf)[(int) ipos];
+                    ipos += cvt->rate_incr;
+                    output16 += 1;
+                } /* for */
+                break;
+        } /* switch */
+    } /* if */
+    else
+    {
+            /* 8- or 16-bit sound */
+        switch (*format & 0xFF)
+        {
+            case 8:
+                output8 = cvt->buf + clen;
+
+                ipos = (double) cvt->len_cvt;
+                for (i = clen; i; --i)
+                {
+                    ipos -= cvt->rate_incr;
+                    output8 -= 1;
+                    *output8 = cvt->buf[(int) ipos];
+                } /* for */
+                break;
+
+            case 16:
+                clen &= ~1;
+                output16 = (Uint16 *) (cvt->buf + clen);
+                ipos = (double) cvt->len_cvt / 2;
+                for (i = clen / 2; i; --i)
+                {
+                    ipos -= cvt->rate_incr;
+                    output16 -= 1;
+                    *output16 = ((Uint16 *) cvt->buf)[(int) ipos];
+                } /* for */
+                break;
+        } /* switch */
+    } /* else */
+
+    cvt->len_cvt = clen;
+} /* Sound_RateSLOW */
+
+
+int Sound_ConvertAudio(Sound_AudioCVT *cvt)
+{
+    Uint16 format;
+
+        /* Make sure there's data to convert */
+    if (cvt->buf == NULL)
+    {
+        Sound_SetError("No buffer allocated for conversion");
+        return(-1);
+    } /* if */
+
+        /* Return okay if no conversion is necessary */
+    cvt->len_cvt = cvt->len;
+    if (cvt->filters[0] == NULL)
+        return(0);
+
+        /* Set up the conversion and go! */
+    format = cvt->src_format;
+    for (cvt->filter_index = 0; cvt->filters[cvt->filter_index];
+         cvt->filter_index++)
+    {
+        cvt->filters[cvt->filter_index](cvt, &format);
+    }
+    return(0);
+} /* Sound_ConvertAudio */
+
+
+/*
+ * Creates a set of audio filters to convert from one format to another. 
+ * Returns -1 if the format conversion is not supported, or 1 if the
+ * audio filter is set up.
+ */
+
+int Sound_BuildAudioCVT(Sound_AudioCVT *cvt,
+                        Uint16 src_format, Uint8 src_channels, Uint32 src_rate,
+                        Uint16 dst_format, Uint8 dst_channels, Uint32 dst_rate)
+{
+        /* Start off with no conversion necessary */
+    cvt->needed = 0;
+    cvt->filter_index = 0;
+    cvt->filters[0] = NULL;
+    cvt->len_mult = 1;
+    cvt->len_ratio = 1.0;
+
+        /* First filter:  Endian conversion from src to dst */
+    if ((src_format & 0x1000) != (dst_format & 0x1000) &&
+       ((src_format & 0xff) != 8))
+    {
+        SNDDBG(("Adding filter: Sound_ConvertEndian\n"));
+        cvt->filters[cvt->filter_index++] = Sound_ConvertEndian;
+    } /* if */
+	
+        /* Second filter: Sign conversion -- signed/unsigned */
+    if ((src_format & 0x8000) != (dst_format & 0x8000))
+    {
+        SNDDBG(("Adding filter: Sound_ConvertSign\n"));
+        cvt->filters[cvt->filter_index++] = Sound_ConvertSign;
+    } /* if */
+
+        /* Next filter:  Convert 16 bit <--> 8 bit PCM. */
+    if ((src_format & 0xFF) != (dst_format & 0xFF))
+    {
+        switch (dst_format & 0x10FF)
+        {
+            case AUDIO_U8:
+                SNDDBG(("Adding filter: Sound_Convert8\n"));
+                cvt->filters[cvt->filter_index++] = Sound_Convert8;
+                cvt->len_ratio /= 2;
+                break;
+
+            case AUDIO_U16LSB:
+                SNDDBG(("Adding filter: Sound_Convert16LSB\n"));
+                cvt->filters[cvt->filter_index++] = Sound_Convert16LSB;
+                cvt->len_mult *= 2;
+                cvt->len_ratio *= 2;
+                break;
+
+            case AUDIO_U16MSB:
+                SNDDBG(("Adding filter: Sound_Convert16MSB\n"));
+                cvt->filters[cvt->filter_index++] = Sound_Convert16MSB;
+                cvt->len_mult *= 2;
+                cvt->len_ratio *= 2;
+                break;
+        } /* switch */
+    } /* if */
+
+        /* Next filter:  Mono/Stereo conversion */
+    if (src_channels != dst_channels)
+    {
+        while ((src_channels * 2) <= dst_channels)
+        {
+            SNDDBG(("Adding filter: Sound_ConvertStereo\n"));
+            cvt->filters[cvt->filter_index++] = Sound_ConvertStereo;
+            cvt->len_mult *= 2;
+            src_channels *= 2;
+            cvt->len_ratio *= 2;
+        } /* while */
+
+        /* This assumes that 4 channel audio is in the format:
+         *     Left {front/back} + Right {front/back}
+         * so converting to L/R stereo works properly.
+         */
+        while (((src_channels % 2) == 0) &&
+               ((src_channels / 2) >= dst_channels))
+        {
+            SNDDBG(("Adding filter: Sound_ConvertMono\n"));
+            cvt->filters[cvt->filter_index++] = Sound_ConvertMono;
+            src_channels /= 2;
+            cvt->len_ratio /= 2;
+        } /* while */
+
+        if ( src_channels != dst_channels ) {
+            /* Uh oh.. */;
+        } /* if */
+    } /* if */
+
+    /* Do rate conversion */
+    cvt->rate_incr = 0.0;
+    if ((src_rate / 100) != (dst_rate / 100))
+    {
+        Uint32 hi_rate, lo_rate;
+        int len_mult;
+        double len_ratio;
+        void (*rate_cvt)(Sound_AudioCVT *cvt, Uint16 *format);
+
+        if (src_rate > dst_rate)
+        {
+            hi_rate = src_rate;
+            lo_rate = dst_rate;
+            SNDDBG(("Adding filter: Sound_RateDIV2\n"));
+            rate_cvt = Sound_RateDIV2;
+            len_mult = 1;
+            len_ratio = 0.5;
+        } /* if */
+        else
+        {
+            hi_rate = dst_rate;
+            lo_rate = src_rate;
+            SNDDBG(("Adding filter: Sound_RateMUL2\n"));
+            rate_cvt = Sound_RateMUL2;
+            len_mult = 2;
+            len_ratio = 2.0;
+        } /* else */
+
+            /* If hi_rate = lo_rate*2^x then conversion is easy */
+        while (((lo_rate * 2) / 100) <= (hi_rate / 100))
+        {
+            cvt->filters[cvt->filter_index++] = rate_cvt;
+            cvt->len_mult *= len_mult;
+            lo_rate *= 2;
+            cvt->len_ratio *= len_ratio;
+        } /* while */
+
+            /* We may need a slow conversion here to finish up */
+        if ((lo_rate / 100) != (hi_rate / 100))
+        {
+            if (src_rate < dst_rate)
+            {
+                cvt->rate_incr = (double) lo_rate / hi_rate;
+                cvt->len_mult *= 2;
+                cvt->len_ratio /= cvt->rate_incr;
+            } /* if */
+            else
+            {
+                cvt->rate_incr = (double) hi_rate / lo_rate;
+                cvt->len_ratio *= cvt->rate_incr;
+            } /* else */
+            SNDDBG(("Adding filter: Sound_RateSLOW\n"));
+            cvt->filters[cvt->filter_index++] = Sound_RateSLOW;
+        } /* if */
+    } /* if */
+
+        /* Set up the filter information */
+    if (cvt->filter_index != 0)
+    {
+        cvt->needed = 1;
+        cvt->src_format = src_format;
+        cvt->dst_format = dst_format;
+        cvt->len = 0;
+        cvt->buf = NULL;
+        cvt->filters[cvt->filter_index] = NULL;
+    } /* if */
+
+    return(cvt->needed);
+} /* Sound_BuildAudioCVT */