diff --git a/tools/adpcm.c b/tools/adpcm.c
new file mode 100644
index 0000000..2c3be24
--- /dev/null
+++ b/tools/adpcm.c
@@ -0,0 +1,147 @@
+#include <stdint.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <errno.h>
+#include <string.h>
+
+static inline int clamp(int x, int low, int high)
+{
+  if (x > high)
+    return high;
+  if (x < low)
+    return low;
+  return x;
+}
+
+static inline int ymz_step(uint8_t step, int16_t * history, int16_t * step_size)
+{
+  static const int step_table[8] = {
+    230, 230, 230, 230, 307, 409, 512, 614
+  };
+
+  int sign = step & 8;
+  int delta = step & 7;
+  int diff = ((1 + (delta << 1)) * *step_size) >> 3;
+  int newval = *history;
+  int nstep = (step_table[delta] * *step_size) >> 8;
+  diff = clamp(diff, 0, 32767);
+  if (sign > 0)
+    newval -= diff;
+  else
+    newval += diff;
+  *step_size = clamp(nstep, 127, 24576);
+  *history = newval = clamp(newval, -32768, 32767);
+  return newval;
+}
+
+void adpcm_encode(int16_t * buffer, uint8_t * outbuffer, int len)
+{
+  int16_t step_size = 127;
+  int16_t history = 0;
+  uint8_t buf_sample = 0, nibble = 0;
+  unsigned int adpcm_sample;
+
+  for (int i = 0; i < len; i++) {
+    //int step = ((*buffer++) & -8) - history;
+    int step = *buffer++ - history;
+    adpcm_sample = (abs(step) << 16) / (step_size << 14);
+    adpcm_sample = clamp(adpcm_sample, 0, 7);
+    if(step < 0)
+      adpcm_sample |= 8;
+    if(!nibble)
+      *outbuffer++ = buf_sample | (adpcm_sample << 4);
+    else
+      buf_sample = (adpcm_sample & 15);
+    nibble ^= 1;
+    ymz_step(adpcm_sample, &history, &step_size);
+  }
+}
+
+int read_file(const char * filename, uint8_t ** buf, uint32_t * size_out)
+{
+  FILE * file = fopen(filename, "rb");
+  if (file == NULL) {
+    fprintf(stderr, "fopen(\"%s\", \"rb\"): %s\n", filename, strerror(errno));
+    return -1;
+  }
+
+  int ret;
+  ret = fseek(file, 0L, SEEK_END);
+  if (ret < 0) {
+    fprintf(stderr, "fseek(SEEK_END)");
+    return -1;
+  }
+
+  long offset = ftell(file);
+  if (offset < 0) {
+    fprintf(stderr, "ftell");
+    return -1;
+  }
+  size_t size = offset;
+
+  ret = fseek(file, 0L, SEEK_SET);
+  if (ret < 0) {
+    fprintf(stderr, "fseek(SEEK_SET)");
+    return -1;
+  }
+
+  fprintf(stderr, "read_file: %s size %ld\n", filename, size);
+  *buf = (uint8_t *)malloc(size);
+  size_t fread_size = fread(*buf, 1, size, file);
+  if (fread_size != size) {
+    fprintf(stderr, "fread `%s` short read: %" PRIu64 " ; expected: %" PRIu64 "\n", filename, fread_size, size);
+    return -1;
+  }
+
+  ret = fclose(file);
+  if (ret < 0) {
+    fprintf(stderr, "fclose");
+    return -1;
+  }
+
+  *size_out = size;
+
+  return 0;
+}
+
+int write_file(const char * filename, const uint8_t * buf, uint32_t size)
+{
+  FILE * file = fopen(filename, "wb");
+  if (file == NULL) {
+    fprintf(stderr, "fopen(\"%s\", \"wb\"): %s\n", filename, strerror(errno));
+    return -1;
+  }
+
+  size_t write_size = fwrite(buf, 1, size, file);
+  if (write_size != size) {
+    fprintf(stderr, "fwrite: %d %ld %s\n", size, write_size, strerror(errno));
+    return -1;
+  }
+
+  int ret = fclose(file);
+  if (ret < 0) {
+    fprintf(stderr, "fclose");
+    return -1;
+  }
+
+  return 0;
+}
+
+int main(int argc, char * argv[])
+{
+  assert(argc == 3);
+
+  uint8_t * buf;
+  int size;
+  int ret = read_file(argv[1], &buf, &size);
+  assert(ret == 0);
+
+  uint8_t * out = malloc(size / 4);
+
+  adpcm_encode((uint16_t *)buf, out, size / 2);
+
+  ret = write_file(argv[2], out, size / 4);
+  assert(ret == 0);
+}