source: mainline/uspace/lib/trackmod/trackmod.c@ b7fd2a0

/*
 * Copyright (c) 2014 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/** @addtogroup trackmod
 * @{
 */
/**
 * @file Tracker module handling library.
 */

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

#include "macros.h"
#include "protracker.h"
#include "trackmod.h"
#include "xm.h"

/** Tunables */
enum {
        amp_factor = 16
};

/** Standard definitions set in stone */
enum {
        /** Base sample clock */
        base_clock = 8363 * 428,
        /** Maximum sample volume */
        vol_max = 64,
        /** Minimum period */
        period_min = 113,
        /** Maxium period */
        period_max = 856
};

/** Table for finetune computation.
  *
  * Finetune is a number ft in [-8 .. 7]. The pitch should be adjusted by
  * ft/8 semitones. To adjust pitch by 1/8 semitone down we can mutiply the
  * period by 2^(1/12/8) =. 1.0072, one semitone up: 2^-(1/12/8) =. 0.9928,
  * to adjust by ft/8 semitones, multiply by 2^(-ft/12/8).
  *
  * finetune_factor[ft] := 10000 * 2^(-ft/12/8)
  * res_period = clip(period * fineture_factor[ft+8] / 10000)
  */
static unsigned finetune_factor[16] = {
        10595, 10518, 10443, 10368, 10293, 10219, 10145, 10072,
        10000,  9928,  9857,  9786,  9715,  9645,  9576,  9507
};

static unsigned period_table[12 * 8] = {
     907,900,894,887,881,875,868,862,856,850,844,838,832,826,820,814,
     808,802,796,791,785,779,774,768,762,757,752,746,741,736,730,725,
     720,715,709,704,699,694,689,684,678,675,670,665,660,655,651,646,
     640,636,632,628,623,619,614,610,604,601,597,592,588,584,580,575,
     570,567,563,559,555,551,547,543,538,535,532,528,524,520,516,513,
     508,505,502,498,494,491,487,484,480,477,474,470,467,463,460,457
};

static size_t trackmod_get_next_ord_idx(trackmod_modplay_t *);

/** Destroy sample.
 *
 * @param sample Sample
 */
static void trackmod_sample_destroy(trackmod_sample_t *sample)
{
        free(sample->data);
}

/** Destroy instrument.
 *
 * @param instr Intrument
 */
static void trackmod_instr_destroy(trackmod_instr_t *instr)
{
        size_t i;

        for (i = 0; i < instr->samples; i++)
                trackmod_sample_destroy(&instr->sample[i]);
}

/** Destroy pattern.
 *
 * @param pattern Pattern
 */
static void trackmod_pattern_destroy(trackmod_pattern_t *pattern)
{
        free(pattern->data);
}

/** Create new empty module structure.
 *
 * @return New module
 */
trackmod_module_t *trackmod_module_new(void)
{
        return calloc(1, sizeof(trackmod_module_t));
}

/** Destroy module.
 *
 * @param module Module
 */
void trackmod_module_destroy(trackmod_module_t *module)
{
        size_t i;

        /* Destroy samples */
        if (module->instr != NULL) {
                for (i = 0; i < module->instrs; i++)
                        trackmod_instr_destroy(&module->instr[i]);
                free(module->instr);
        }

        /* Destroy patterns */
        if (module->pattern != NULL) {
                for (i = 0; i < module->patterns; i++)
                        trackmod_pattern_destroy(&module->pattern[i]);
                free(module->pattern);
        }

        free(module->ord_list);
        free(module);
}

errno_t trackmod_module_load(char *fname, trackmod_module_t **rmodule)
{
        errno_t rc;

        rc = trackmod_xm_load(fname, rmodule);
        if (rc == EOK)
                return EOK;

        rc = trackmod_protracker_load(fname, rmodule);
        return rc;
}


/** Return current pattern.
 *
 * @param modplay Module playback
 * @return        Pattern
 */
static trackmod_pattern_t *trackmod_cur_pattern(trackmod_modplay_t *modplay)
{
        unsigned pat_idx;

        pat_idx = modplay->module->ord_list[modplay->ord_idx];
        return &modplay->module->pattern[pat_idx];
}

/** Decode pattern cell.
 *
 * @param pattern Pattern
 * @param row     Row number
 * @param channel Channel number
 * @param cell    Place to store decoded cell
 */
static void trackmod_pattern_get_cell(trackmod_pattern_t *pattern,
    size_t row, size_t channel, trackmod_cell_t *cell)
{
        *cell = pattern->data[row * pattern->channels + channel];
}

/** Compute floor(a / b), and the remainder.
 *
 * Unlike standard integer division this rounds towars negative infinity,
 * not towards zero.
 *
 * @param a Dividend
 * @param b Divisor
 * @param quot Place to store 'quotient' (floor (a/b))
 * @param rem Place to store 'remainder' (a - floor(a/b) * b)
 */
static void divmod_floor(int a, int b, int *quot, int *rem)
{
        if (b < 0) {
                a = -a;
                b = -b;
        }

        if (a >= 0) {
                *quot = a / b;
                *rem = a % b;
        } else {
                *quot = - (-a + (b - 1)) / b;
                *rem = a - (*quot * b);
        }
}

/** Process note (period)
 *
 * @param modplay Module playback
 * @param i       Channel number
 * @param cell    Cell
 */
static void trackmod_process_note(trackmod_modplay_t *modplay, size_t i,
    trackmod_cell_t *cell)
{
        trackmod_chan_t *chan = &modplay->chan[i];
        int period;
        int pitch;
        int octave;
        int opitch;

        if (chan->sample == NULL)
                return;

        if (cell->period == 0) {
                pitch = 8 * (cell->note + chan->sample->rel_note) +
                    chan->sample->finetune;
                divmod_floor(pitch, 8 * 12, &octave, &opitch);

                if (octave >= 0)
                        period = period_table[opitch] * 8 / (1 << octave);
                else
                        period = period_table[opitch] * 8 * (1 << (-octave));
        } else {
                period = cell->period;
                period = period *
                    finetune_factor[chan->sample->finetune + 8] / 10000;
                if (period > period_max)
                        period = period_max;
                if (period < period_min)
                        period = period_min;
        }

        chan->period_new = period;
}

/** Process instrument number (this is what triggers the note playback)
 *
 * @param modplay Module playback
 * @param i       Channel number
 * @param cell    Cell
 */
static void trackmod_process_instr(trackmod_modplay_t *modplay, size_t i,
    trackmod_cell_t *cell)
{
        trackmod_chan_t *chan = &modplay->chan[i];
        trackmod_instr_t *instr;
        size_t iidx;
        size_t sidx;

        if (cell->instr == 0)
                return;

        iidx = (cell->instr - 1) % modplay->module->instrs;
        instr = &modplay->module->instr[iidx];
        sidx = instr->key_smp[cell->note] % instr->samples;
        chan->sample = &instr->sample[sidx];
        chan->smp_pos = 0;
        chan->lsmp = 0;

        chan->volume = modplay->chan[i].sample->def_vol;
}

/** Process keyoff note
 *
 * @param modplay Module playback
 * @param i       Channel number
 * @param cell    Cell
 */
static void trackmod_process_keyoff_note(trackmod_modplay_t *modplay, size_t i)
{
        trackmod_chan_t *chan = &modplay->chan[i];

        chan->sample = NULL;
        chan->period = 0;
        chan->smp_pos = 0;
        chan->lsmp = 0;
}

/** Process Set volume effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_set_volume(trackmod_modplay_t *modplay, size_t chan,
    uint8_t param)
{
        modplay->chan[chan].volume = param % (vol_max + 1);
}

/** Process Pattern break effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_pattern_break(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        size_t next_idx;
        trackmod_pattern_t *next_pat;
        unsigned row;

        /* Strangely the parameter is BCD */
        row = (param >> 4) * 10 + (param & 0xf);

        next_idx = trackmod_get_next_ord_idx(modplay);
        next_pat = &modplay->module->pattern[next_idx]; 

        modplay->pat_break = true;
        modplay->pat_break_row = row % next_pat->rows;
}

/** Process Set speed effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_set_speed(trackmod_modplay_t *modplay, size_t chan,
    uint8_t param)
{
        if (param > 0 && param < 32)
                modplay->tpr = param;
        else if (param > 0)
                modplay->bpm = param;
}

/** Process Fine volume slide down effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_fine_vol_slide_down(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        int nv;

        nv = modplay->chan[chan].volume - param;
        if (nv < 0)
                nv = 0;
        modplay->chan[chan].volume = nv;
}

/** Process Fine volume slide up effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_fine_vol_slide_up(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        int nv;

        nv = modplay->chan[chan].volume + param;
        if (nv > vol_max)
                nv = vol_max;
        modplay->chan[chan].volume = nv;
}

/** Process Volume slide effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_vol_slide(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        if ((param & 0xf0) != 0)
                modplay->chan[chan].vol_slide = param >> 4;
        else
                modplay->chan[chan].vol_slide = -(int)(param & 0xf);
}

/** Process Volume slide down effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_vol_slide_down(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param4)
{
        modplay->chan[chan].vol_slide = -(int)param4;
}

/** Process Volume slide up effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_vol_slide_up(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param4)
{
        modplay->chan[chan].vol_slide = param4;
}

/** Process Fine portamento down effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_fine_porta_down(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        int np;

        np = modplay->chan[chan].period + param;
        if (np > period_max)
                np = period_max;
        modplay->chan[chan].period = np;
}

/** Process Fine portamento up effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_fine_porta_up(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        int np;

        np = modplay->chan[chan].period - param;
        if (np < period_min)
                np = period_min;
        modplay->chan[chan].period = np;
}

/** Process Portamento down effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_porta_down(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        modplay->chan[chan].portamento = -(int)param;
}

/** Process Portamento up effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_porta_up(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        modplay->chan[chan].portamento = param;
}

/** Process Tone portamento effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param param   Effect parameter
 */
static void trackmod_effect_tone_porta(trackmod_modplay_t *modplay,
    size_t chan, uint8_t param)
{
        /* Set up tone portamento effect */
        modplay->chan[chan].portamento = param;
        if (modplay->chan[chan].period_new != 0)
                modplay->chan[chan].period_tgt = modplay->chan[chan].period_new;

        /* Prevent going directly to new period */
        modplay->chan[chan].period_new = 0;
}

/** Process volume column.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param cell    Cell
 */
static void trackmod_process_volume(trackmod_modplay_t *modplay, size_t chan,
    trackmod_cell_t *cell)
{
        uint8_t param4;

        if (cell->volume >= 0x10 && cell->volume <= 0x10 + vol_max)
                trackmod_effect_set_volume(modplay, chan, cell->volume - 0x10);

        param4 = cell->volume & 0xf;

        switch (cell->volume & 0xf0) {
        case 0x60:
                trackmod_effect_vol_slide_down(modplay, chan, param4);
                break;
        case 0x70:
                trackmod_effect_vol_slide_up(modplay, chan, param4);
                break;
        case 0x80:
                trackmod_effect_fine_vol_slide_down(modplay, chan, param4);
                break;
        case 0x90:
                trackmod_effect_fine_vol_slide_up(modplay, chan, param4);
                break;
        case 0xf0:
                trackmod_effect_tone_porta(modplay, chan, param4 << 4);
                break;
        default:
                break;
        }
}

/** Process effect.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param cell    Cell
 */
static void trackmod_process_effect(trackmod_modplay_t *modplay, size_t chan,
    trackmod_cell_t *cell)
{
        uint8_t param8;
        uint8_t param4;

        param8 = cell->effect & 0xff;

        switch (cell->effect & 0xf00) {
        case 0x100:
                trackmod_effect_porta_up(modplay, chan, param8);
                break;
        case 0x200:
                trackmod_effect_porta_down(modplay, chan, param8);
                break;
        case 0x300:
                trackmod_effect_tone_porta(modplay, chan, param8);
                break;
        case 0xa00:
                trackmod_effect_vol_slide(modplay, chan, param8);
                break;
        case 0xc00:
                trackmod_effect_set_volume(modplay, chan, param8);
                break;
        case 0xd00:
                trackmod_effect_pattern_break(modplay, chan, param8);
                break;
        case 0xf00:
                trackmod_effect_set_speed(modplay, chan, param8);
                break;
        default:
                break;
        }

        param4 = cell->effect & 0xf;

        switch (cell->effect & 0xff0) {
        case 0xe10:
                trackmod_effect_fine_porta_up(modplay, chan, param4);
                break;
        case 0xe20:
                trackmod_effect_fine_porta_down(modplay, chan, param4);
                break;
        case 0xea0:
                trackmod_effect_fine_vol_slide_up(modplay, chan, param4);
                break;
        case 0xeb0:
                trackmod_effect_fine_vol_slide_down(modplay, chan, param4);
                break;
        }
}

/** Process pattern cell.
 *
 * @param modplay Module playback
 * @param chan    Channel number
 * @param cell    Cell
 */
static void trackmod_process_cell(trackmod_modplay_t *modplay, size_t chan,
    trackmod_cell_t *cell)
{
        modplay->chan[chan].period_new = 0;

        trackmod_process_instr(modplay, chan, cell);

        if (cell->period != 0 || (cell->note != 0 && cell->note != keyoff_note)) {
                trackmod_process_note(modplay, chan, cell);
        } else if (cell->note == keyoff_note && cell->instr == 0) {
                trackmod_process_keyoff_note(modplay, chan);
        }

        trackmod_process_volume(modplay, chan, cell);
        trackmod_process_effect(modplay, chan, cell);

        if (modplay->chan[chan].period_new != 0)
                modplay->chan[chan].period = modplay->chan[chan].period_new;
}

/** Process pattern row.
 *
 * @param modplay Module playback
 */
static void trackmod_process_row(trackmod_modplay_t *modplay)
{
        trackmod_pattern_t *pattern;
        trackmod_cell_t cell;
        size_t i;

        pattern = trackmod_cur_pattern(modplay);

        if (modplay->debug)
                printf("%02zx: ", modplay->row);

        for (i = 0; i < modplay->module->channels; i++) {
                trackmod_pattern_get_cell(pattern, modplay->row, i, &cell);

                if (modplay->debug) {
                        printf("%4d %02x %02x %03x |", cell.period ?
                            cell.period : cell.note, cell.instr,
                            cell.volume, cell.effect);
                }

                trackmod_process_cell(modplay, i, &cell);
        }

        if (modplay->debug)
                printf("\n");
}

/** Get next order list index.
 *
 * @param modplay Module playback
 * @return        Next order list index
 */
static size_t trackmod_get_next_ord_idx(trackmod_modplay_t *modplay)
{
        size_t ord_idx;

        ord_idx = modplay->ord_idx + 1;
        if (ord_idx >= modplay->module->ord_list_len)
                ord_idx = modplay->module->restart_pos;

        return ord_idx;
}

/** Advance to next pattern.
 *
 * @param modplay Module playback
 */
static void trackmod_next_pattern(trackmod_modplay_t *modplay)
{
        if (modplay->debug)
                printf("Next pattern\n");

        modplay->row = 0;
        modplay->ord_idx = trackmod_get_next_ord_idx(modplay);

        /* If we are doing a pattern break */
        if (modplay->pat_break) {
                modplay->row = modplay->pat_break_row;
                modplay->pat_break = false;
        }
}

/** Clear effects at end of row. */
static void trackmod_clear_effects(trackmod_modplay_t *modplay)
{
        size_t i;

        for (i = 0; i < modplay->module->channels; i++) {
                modplay->chan[i].vol_slide = 0;
                modplay->chan[i].portamento = 0;
        }
}

/** Process effects at beginning of tick. */
static void trackmod_process_tick(trackmod_modplay_t *modplay)
{
        trackmod_chan_t *chan;
        size_t i;
        int nv;
        int np;

        for (i = 0; i < modplay->module->channels; i++) {
                chan = &modplay->chan[i];

                /* Volume slides */
                nv = (int)chan->volume + chan->vol_slide;
                if (nv < 0)
                        nv = 0;
                if (nv > vol_max)
                        nv = vol_max;

                chan->volume = nv;

                /* Portamentos */
                if (chan->period_tgt == 0) {
                        /* Up or down portamento */
                        np = (int)chan->period - chan->portamento;
                } else {
                        /* Tone portamento */
                        if (chan->period_tgt < chan->period)
                                np = max((int)chan->period_tgt, (int)chan->period - chan->portamento);
                        else
                                np = min((int)chan->period_tgt, (int)chan->period + chan->portamento);
                }

/*              if (np < period_min)
                        np = period_min;
                if (np > period_max)
                        np = period_max;
*/
                modplay->chan[i].period = np;
        }
}

/** Advance to next row.
 *
 * @param modplay Module playback
 */
static void trackmod_next_row(trackmod_modplay_t *modplay)
{
        trackmod_pattern_t *pattern;

        /* Clear effect state at end of row */
        trackmod_clear_effects(modplay);

        pattern = trackmod_cur_pattern(modplay);

        modplay->tick = 0;
        ++modplay->row;
        if (modplay->row >= pattern->rows || modplay->pat_break)
                trackmod_next_pattern(modplay);

        trackmod_process_tick(modplay);
        trackmod_process_row(modplay);
}

/** Advance to next tick.
 *
 * @param modplay Module playback
 */
static void trackmod_next_tick(trackmod_modplay_t *modplay)
{
        modplay->smp = 0;
        ++modplay->tick;
        if (modplay->tick >= modplay->tpr)
                trackmod_next_row(modplay);
        else
                trackmod_process_tick(modplay);
}

/** Create module playback object.
 *
 * @param module   Module
 * @param smp_freq Sampling frequency
 * @param rmodplay Place to store pointer to module playback object
 */
errno_t trackmod_modplay_create(trackmod_module_t *module,
    unsigned smp_freq, trackmod_modplay_t **rmodplay)
{
        trackmod_modplay_t *modplay = NULL;

        modplay = calloc(1, sizeof(trackmod_modplay_t));
        if (modplay == NULL)
                goto error;

        modplay->module = module;
        modplay->smp_freq = smp_freq;
        modplay->frame_size = sizeof(int16_t);
        modplay->ord_idx = 0;
        modplay->row = 0;
        modplay->tick = 0;
        modplay->smp = 0;

        modplay->tpr = module->def_tpr;
        modplay->bpm = module->def_bpm;

        modplay->chan = calloc(module->channels,
            sizeof(trackmod_chan_t));
        if (modplay->chan == NULL)
                goto error;

        trackmod_process_tick(modplay);
        trackmod_process_row(modplay);

        *rmodplay = modplay;
        return EOK;
error:
        if (modplay != NULL)
                free(modplay->chan);
        free(modplay);
        return ENOMEM;
}

/** Destroy module playback object.
 *
 * @param modplay Module playback
 */
void trackmod_modplay_destroy(trackmod_modplay_t *modplay)
{
        free(modplay->chan);
        free(modplay);
}

/** Get number of samples per tick.
 *
 * @param modplay Module playback
 * @return        Number of samples per tick
 */
static size_t samples_per_tick(trackmod_modplay_t *modplay)
{
        return modplay->smp_freq * 10 / 4 / modplay->bpm;
}

/** Get number of samples remaining in current tick.
 *
 * @param modplay Module playback
 * @return        Number of remaining samples in tick
 */
static size_t samples_remain_tick(trackmod_modplay_t *modplay)
{
        /* XXX Integer samples per tick is a simplification */
        return samples_per_tick(modplay) - modplay->smp;
}

/** Get sample frame.
 *
 * Get frame at the specified sample position.
 *
 * @param sample Sample
 * @param pos    Position (frame index)
 * @return       Frame value
 */
int trackmod_sample_get_frame(trackmod_sample_t *sample, size_t pos)
{
        int8_t *i8p;
        int16_t *i16p;

        if (sample->bytes_smp == 1) {
                i8p = (int8_t *)sample->data;
                return i8p[pos];
        } else {
                /* chan->sample->bytes_smp == 2 */
                i16p = (int16_t *)sample->data;
                return i16p[pos] / 256; /* XXX Retain full precision */
        }
}

/** Advance sample position to next frame.
 *
 * @param chan Channel playback
 */
static void chan_smp_next_frame(trackmod_chan_t *chan)
{
        chan->lsmp = trackmod_sample_get_frame(chan->sample, chan->smp_pos);
        ++chan->smp_pos;

        switch (chan->sample->loop_type) {
        case tl_pingpong_loop:
                /** XXX Pingpong loop */
        case tl_no_loop:
                /* No loop */
                if (chan->smp_pos >= chan->sample->length) {
                        chan->sample = NULL;
                        chan->smp_pos = 0;
                }
                break;
        case tl_forward_loop:
                /** Forward loop */
                if (chan->smp_pos >= chan->sample->loop_start +
                    chan->sample->loop_len) {
                        chan->smp_pos = chan->sample->loop_start;
                }
        }
}

/** Render next sample on channel.
 *
 * @param modplay Module playback
 * @param cidx    Channel number
 * @return        Sample value
 */
static int trackmod_chan_next_sample(trackmod_modplay_t *modplay,
    size_t cidx)
{
        int sl, sn;
        int period, clk;
        int s;

        trackmod_chan_t *chan = &modplay->chan[cidx];

        if (chan->sample == NULL || chan->period == 0)
                return 0;

        /*
         * Linear interpolation. Note this is slightly simplified:
         * We ignore the half-sample offset and the boundary condition
         * at the end of the sample (we should extend with zero).
         */
        sl = (int)chan->lsmp * amp_factor * chan->volume / vol_max;
        sn = (int)trackmod_sample_get_frame(chan->sample, chan->smp_pos) *
            amp_factor * chan->volume / vol_max;

        period = (int)chan->period;
        clk = (int)chan->smp_clk;

        s = (sl * (period - clk) + sn * clk) / period;

        chan->smp_clk += base_clock / modplay->smp_freq;
        while (chan->sample != NULL && chan->smp_clk >= chan->period) {
                chan->smp_clk -= chan->period;
                chan_smp_next_frame(chan);
        }

        return s;
}

/** Render a segment of samples contained entirely within a tick.
 *
 * @param modplay Module playback
 * @param buffer  Buffer for storing audio data
 * @param bufsize Size of @a buffer in bytes
 */
static void get_samples_within_tick(trackmod_modplay_t *modplay,
    void *buffer, size_t bufsize)
{
        size_t nsamples;
        size_t smpidx;
        size_t chan;
        int s;

        nsamples = bufsize / modplay->frame_size;

        for (smpidx = 0; smpidx < nsamples; smpidx++) {
                s = 0;
                for (chan = 0; chan < modplay->module->channels; chan++) {
                        s += trackmod_chan_next_sample(modplay, chan);
                }

                ((int16_t *)buffer)[smpidx] = s;
        }

        modplay->smp += nsamples;
}

/** Render a segment of samples.
 *
 * @param modplay Module playback
 * @param buffer  Buffer for storing audio data
 * @param bufsize Size of @a buffer in bytes
 */
void trackmod_modplay_get_samples(trackmod_modplay_t *modplay,
    void *buffer, size_t bufsize)
{
        size_t nsamples;
        size_t rsmp;
        size_t now;

        nsamples = bufsize / modplay->frame_size;
        while (nsamples > 0) {
                rsmp = samples_remain_tick(modplay);
                if (rsmp == 0)
                        trackmod_next_tick(modplay);

                rsmp = samples_remain_tick(modplay);
                now = min(rsmp, nsamples);

                get_samples_within_tick(modplay, buffer,
                    now * modplay->frame_size);
                nsamples -= now;
                buffer += now * modplay->frame_size;
        }
}

/** @}
 */