Implement a bridge to call Sointu from Go language.

The main interface is render_samples function, which renders several samples in one call,
to limit the number of calls from Go to C. This is compiled into a library, which is then
linked and called from bridge.go.

tests/test_render_samples.c

@@ -0,0 +1,45 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include "../include/sointu.h"
+
+#if UINTPTR_MAX == 0xffffffff // are we 32-bit?
+#if defined(__clang__) || defined(__GNUC__)
+#define CALLCONV __attribute__ ((stdcall))
+#elif defined(_WIN32)
+#define CALLCONV __stdcall // on 32-bit platforms, we just use stdcall, as all know it
+#endif
+#else // 64-bit
+#define CALLCONV  // the asm will use honor honor correct x64 ABI on all 64-bit platforms
+#endif
+
+#define BPM 100
+#define SAMPLE_RATE 44100
+#define TOTAL_ROWS 16
+#define SAMPLES_PER_ROW SAMPLE_RATE * 4 * 60 / (BPM * 16)
+const int su_max_samples = SAMPLES_PER_ROW * TOTAL_ROWS;
+
+void CALLCONV su_render(float* buffer) {
+    SynthState* synthState;  
+    const unsigned char commands[] = { su_envelope_id, // MONO
+                                       su_envelope_id, // MONO
+                                       su_out_id + 1,  // STEREO
+                                       su_advance_id };// MONO
+    const unsigned char values[] = { 64, 64, 64, 80, 128, // envelope 1
+                                     95, 64, 64, 80, 128, // envelope 2
+                                     128};
+    int retval;
+    synthState = malloc(sizeof(SynthState));
+    memset(synthState, 0, sizeof(SynthState));
+    memcpy(synthState->Commands, commands, sizeof(commands));
+    memcpy(synthState->Values, values, sizeof(values));
+    synthState->RandSeed = 1;
+    synthState->RowLen = INT32_MAX;
+    synthState->NumVoices = 1;
+    synthState->Synth.Voices[0].Note = 64;
+    retval = su_render_samples(synthState, su_max_samples / 2, buffer);
+    synthState->Synth.Voices[0].Release++;
+    buffer = buffer + su_max_samples;
+    retval = su_render_samples(synthState, su_max_samples / 2, buffer);
+    free(synthState);
+	return;
+}