2021-01-01 20:44:05 (UTC-03:00)

Marcel Rodrigues <marcelgmr@gmail.com>

first commit

minimal core with sawtooth and sine waves
no front-end
no back-end

diff --git a/qms.c b/qms.c
new file mode 100644
index 0000000..735e4e6
--- /dev/null
+++ b/qms.c
@@ -0,0 +1,122 @@
+#include "qms.h"
+
+typedef struct TrackState {
+    int pac;   /* < NPACS */
+    int vol;   /* 0-127 */
+    int pan;   /* (-64)-(+63) */
+} TrackState;
+
+typedef struct VoiceState {
+    unsigned int phase_acc;   /* fixed point with NEXP.NEXP precision */
+    unsigned int phase_step;  /* fixed point with NEXP.NEXP precision */
+    int velocity;    /* 0-127 */
+    /* int note_age; */
+} VoiceState;
+
+static int16_t wavetables[NPACS][N];
+static TrackState tracks[NTRACKS];
+static VoiceState voices[NTRACKS][NVOICES];
+
+/* integer frequencies of MIDI notes 0-11 multiplied by N */
+/* to be used as fixed point with NEXP.NEXP precision */
+/* python: [int(440 * 2**((m-69)/12) * N +0.5) for m in range(12)] */
+static int freq[12] =
+  {16744, 17740, 18795, 19912, 21096, 22351,
+   23680, 25088, 26580, 28160, 29834, 31609};
+
+/* sine approximation using Bhaskara I's formula
+ * input is in [0;2048]
+ * output is in [-INT16_MAX;INT16_MAX] */
+static int16_t
+sinb1(unsigned int i)
+{
+    uint32_t c, n, d;
+    int16_t s = 1 - (i >> 10 << 1);
+    i &= 1023;
+    c = i*(46080 - 45*i);
+    n = 360*c;
+    d = 162005 - (90*c >> 15);
+    return s * (int16_t) (n/d);
+}
+
+void
+qms_init()
+{
+    unsigned int i;
+    int32_t tmp;
+    for (i = 0; i < N; i++) {
+        /* sawtooth */
+        tmp = (i * INT16_MAX >> (NEXP-1)) - INT16_MAX;
+        wavetables[0][i] = (int16_t) tmp;
+    }
+    for (i = 0; i < N; i++) {
+        /* sine */
+        wavetables[1][i] = sinb1(i);
+    }
+}
+
+void
+qms_setpac(int track, int pac)
+{
+    tracks[track].pac = pac;
+}
+
+void
+qms_setvolume(int track, int midivol)
+{
+    tracks[track].vol = midivol;
+}
+
+void
+qms_setpan(int track, int midipan)
+{
+    tracks[track].pan = midipan - 64;
+}
+
+static int
+midipitch2step(int m)
+{
+    int o, n; /* m = o * 12 + n */
+    for (n = m, o = 0; n >= 12; n -= 12, o++) ;
+    return (freq[n] << (o+NEXP)) / R;
+}
+
+void
+qms_setnote(int track, int voice, int velocity, int midipitch)
+{
+    voices[track][voice].velocity = velocity;
+    voices[track][voice].phase_step = midipitch2step(midipitch);
+}
+
+void
+qms_advance(int nsamples)
+{
+    int32_t left, right;
+    int32_t amp;
+    int16_t *pac;
+    int lvol, rvol; /* 0 - 2^14 */
+    TrackState *track;
+    VoiceState *voice;
+    int ti, vi;
+    for (; nsamples; nsamples--) {
+        left = right = 0;
+        for (ti = 0; ti < NTRACKS; ti++) {
+            track = &tracks[ti];
+            lvol = (63 - track->pan) * track->vol;
+            rvol = (63 + track->pan) * track->vol;
+            pac = wavetables[track->pac];
+            for (vi = 0; vi < NVOICES; vi++) {
+                voice = &voices[ti][vi];
+                amp = pac[voice->phase_acc >> NEXP] * voice->velocity >> 7;
+                left  += amp * lvol >> 14;
+                right += amp * rvol >> 14;
+                voice->phase_acc += voice->phase_step;
+                voice->phase_acc &= (1 << (NEXP << 1)) - 1;
+            }
+        }
+        /* saturate before casting down to 16-bit to avoid bad behavior on overflow */
+        left  =  left < INT16_MIN ? INT16_MIN : ( left > INT16_MAX ? INT16_MAX :  left);
+        right = right < INT16_MIN ? INT16_MIN : (right > INT16_MAX ? INT16_MAX : right);
+        qms_putsample((int16_t) left, (int16_t) right);
+    }
+}

diff --git a/qms.h b/qms.h
new file mode 100644
index 0000000..daa4885
--- /dev/null
+++ b/qms.h
@@ -0,0 +1,21 @@
+#include <stdint.h>
+
+#define NTRACKS     16
+#define NVOICES     8
+
+#define NPACS       2
+
+/* N = 2^NEXP */
+#define NEXP    11
+/* wavetable size in samples */
+#define N       (1 << NEXP)
+/* sample rate in samples per second*/
+#define R       44100
+
+void qms_init();
+void qms_setpac(int track, int pac);
+void qms_setvolume(int track, int midivol);
+void qms_setpan(int track, int midipan);
+void qms_setnote(int track, int voice, int velocity, int midipitch);
+void qms_advance(int nsamples);
+void qms_putsample(int16_t left, int16_t right);