1 files changed, 50 insertions, 0 deletions
diff --git a/lib/vgmstream/src/coding/aica_decoder.c b/lib/vgmstream/src/coding/aica_decoder.c
new file mode 100644
index 0000000000..9bd6b7468b
--- /dev/null
+++ b/lib/vgmstream/src/coding/aica_decoder.c
@@ -0,0 +1,50 @@
+#include "../util.h"
+#include "coding.h"
+
+/* fixed point (.8) amount to scale the current step size by */
+/* part of the same series as used in MS ADPCM "ADPCMTable" */
+static const unsigned int scale_step[16] =
+{
+    230, 230, 230, 230, 307, 409, 512, 614,
+    230, 230, 230, 230, 307, 409, 512, 614
+};
+
+/* expand an unsigned four bit delta to a wider signed range */
+static const int scale_delta[16] = 
+{
+      1,  3,  5,  7,  9, 11, 13, 15,
+     -1, -3, -5, -7, -9,-11,-13,-15
+};
+
+/* Yamaha AICA ADPCM (as seen in Dreamcast) */
+
+void decode_aica(VGMSTREAMCHANNEL * stream, sample * outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do) {
+    int i;
+    int32_t sample_count;
+    int32_t hist1 = stream->adpcm_history1_16;
+    unsigned long step_size = stream->adpcm_step_index;
+
+    for (i=first_sample,sample_count=0; i<first_sample+samples_to_do; i++,sample_count+=channelspacing) {
+        int sample_nibble =
+                (
+                 (unsigned)read_8bit(stream->offset+i/2,stream->streamfile) >>
+                 (i&1?4:0)
+                )&0xf;
+
+        int32_t sample_delta = (int32_t)step_size * scale_delta[sample_nibble];
+        int32_t new_sample;
+
+        new_sample = hist1 + sample_delta/8;
+
+        outbuf[sample_count] = clamp16(new_sample);
+
+        hist1 = outbuf[sample_count];
+
+        step_size = (step_size * scale_step[sample_nibble])/0x100;
+        if (step_size < 0x7f) step_size = 0x7f;
+        if (step_size > 0x6000) step_size = 0x6000;
+    }
+
+    stream->adpcm_history1_16 = hist1;
+    stream->adpcm_step_index = step_size;
+}