Optimise by backpropagating scalar computation in C

1 files changed, 25 insertions, 0 deletions

diff --git a/cbits/backprop.c b/cbits/backprop.c
new file mode 100644
index 0000000..0ca62e3
--- /dev/null
+++ b/cbits/backprop.c
@@ -0,0 +1,25 @@
+// #include <stdio.h>
+#include <stdint.h>
+// #include <inttypes.h>
+
+struct Contrib {
+  int64_t i1;
+  double dx;
+  int64_t i2;
+  double dy;
+};
+
+void ad_dual_hs_backpropagate_double(
+  double *accums,
+  int64_t id_base, int64_t topid, const void *contribs_buf
+) {
+  // fprintf(stderr, "< ci0=%" PRIi64 " topid=%" PRIi64 " >\n", id_base, topid);
+  const struct Contrib *contribs = (const struct Contrib*)contribs_buf;
+
+  for (int64_t i = topid - id_base; i >= 0; i--) {
+    double d = accums[id_base + i];
+    // fprintf(stderr, "ACC i=%" PRIi64 " d=%g C={%" PRIi64 ", %g, %" PRIi64 ", %g}\n", id_base + i, d, contribs[i].i1, contribs[i].dx, contribs[i].i2, contribs[i].dy);
+    if (contribs[i].i1 != -1) accums[contribs[i].i1] += d * contribs[i].dx;
+    if (contribs[i].i2 != -1) accums[contribs[i].i2] += d * contribs[i].dy;
+  }
+}