src/hardware/snd_pc98/sound/psggeng.c

#include    "np2glue.h"
//#include      "compiler.h"
#include        "parts.h"
#include        "sound.h"
#include        "psggen.h"


extern  PSGGENCFG       psggencfg;


void SOUNDCALL psggen_getpcm(PSGGEN psg, SINT32 *pcm, UINT count) {

//      SINT32  noisevol;
        UINT    noisetbl = 0;
        PSGTONE *tone;
        SINT32  samp;
//      UINT    psgvol;
        SINT32  vol;
        UINT    i;
        UINT    noise;

        if ((psg->mixer & 0x3f) == 0) {
                count = min(count, psg->puchicount);
                psg->puchicount -= count;
        }
        if (count == 0) {
                return;
        }
        do {
//              noisevol = 0;
                if (psg->envcnt) {
                        psg->envcnt--;
                        if (psg->envcnt == 0) {
                                psg->envvolcnt--;
                                if (psg->envvolcnt < 0) {
                                        if (psg->envmode & PSGENV_ONESHOT) {
                                                psg->envvol = (psg->envmode & PSGENV_LASTON)?15:0;
                                        }
                                        else {
                                                psg->envvolcnt = 15;
                                                if (!(psg->envmode & PSGENV_ONECYCLE)) {
                                                        psg->envmode ^= PSGENV_INC;
                                                }
                                                psg->envcnt = psg->envmax;
                                                psg->envvol = (psg->envvolcnt ^ psg->envmode) & 0x0f;
                                        }
                                }
                                else {
                                        psg->envcnt = psg->envmax;
                                        psg->envvol = (psg->envvolcnt ^ psg->envmode) & 0x0f;
                                }
                                psg->evol = psggencfg.volume[psg->envvol];
                        }
                }
                UINT8 mixer = psg->mixer;
                if (mixer & 0x38) {
            /* NTS: This code relies on signed integer underflow to determine when to advance
                    the pseudo-random noise generation sequence. It assumes that it can detect
                    SINT32 carry by copying the value, subtracting the original, and then
                    testing to see if the result is larger than the original.

                    Unfortunately, Clang/LLVM break this code by promoting both to long (64-bit)
                    before comparing, which turns the noise into DC bias popping noises.

                    This hack, with long type masks, emulates the original behavior even if the
                    compare is promoted to signed long (64-bit) and allows the noise generation
                    to work even with Clang/LLVM --J.C */
            const long sint32sign = 1L << (((long)(CHAR_BIT * sizeof(long))) - 1L);
            const long sint32mask = sint32sign + 0x7FFFFFFFL;

                        for (i=0; i<(1 << PSGADDEDBIT); i++) {
                                SINT32 countbak;
                                countbak = psg->noise.count;
                                psg->noise.count -= psg->noise.freq;
                                if (((long)psg->noise.count & sint32mask) > ((long)countbak & sint32mask)) {
//                                      psg->noise.base = GETRAND() & (1 << (1 << PSGADDEDBIT));
                                        psg->noise.base = rand_get() & (1 << (1 << PSGADDEDBIT));
                                }
                                noisetbl += psg->noise.base;
                                noisetbl >>= 1;
                        }
                }
                tone = psg->tone;
                PSGTONE *toneterm = tone + 3;
                do {
                        vol = *(tone->pvol);
                        if (vol) {
                                samp = 0;
                                switch(mixer & 9) {
                                        case 0:                                                 // no mix
                                                if (tone->puchi) {
                                                        tone->puchi--;
                                                        samp += vol << PSGADDEDBIT;
                                                }
                                                break;

                                        case 1:                                                 // tone only
                                                for (i=0; i<(1 << PSGADDEDBIT); i++) {
                                                        tone->count += tone->freq;
                                                        samp += vol * ((tone->count>=0)?1:-1);
                                                }
                                                break;

                                        case 8:                                                 // noise only
                                                noise = noisetbl;
                                                for (i=0; i<(1 << PSGADDEDBIT); i++) {
                                                        samp += vol * ((noise & 1)?1:-1);
                                                        noise >>= 1;
                                                }
                                                break;

                                        case 9:
                                                noise = noisetbl;
                                                for (i=0; i<(1 << PSGADDEDBIT); i++) {
                                                        tone->count += tone->freq;
                                                        if ((tone->count >= 0) || (noise & 1)) {
                                                                samp += vol;
                                                        }
                                                        else {
                                                                samp -= vol;
                                                        }
                                                        noise >>= 1;
                                                }
                                                break;
                                }
                                if (!(tone->pan & 1)) {
                                        pcm[0] += samp;
                                }
                                if (!(tone->pan & 2)) {
                                        pcm[1] += samp;
                                }
                        }
                        mixer >>= 1;
                } while(++tone < toneterm);
                pcm += 2;
        } while(--count);
}