ans: Cleanup rans writing routines
* Replace struct rans_sym parameter with values. It only had two entries.
* Document functions.
* Use longer variable names.
TODO: Refactor the unit tests.
Change-Id: Idad65117dab565786697015ef07070e1c308d963
diff --git a/aom_dsp/answriter.h b/aom_dsp/answriter.h
index 4c74cb3..353acf1 100644
--- a/aom_dsp/answriter.h
+++ b/aom_dsp/answriter.h
@@ -124,24 +124,20 @@
ans->state = quotient * ANS_P8_PRECISION + remainder + (value ? p0 : 0);
}
-struct rans_sym {
- aom_cdf_prob prob;
- aom_cdf_prob cum_prob; // not-inclusive
-};
-
-// rANS with normalization
-// sym->prob takes the place of l_s from the paper
-// ANS_P10_PRECISION is m
-static INLINE void rans_write(struct AnsCoder *ans,
- const struct rans_sym *const sym) {
- const aom_cdf_prob p = sym->prob;
- unsigned quot, rem;
- while (ans->state >= L_BASE / RANS_PRECISION * IO_BASE * p) {
+// Encode one symbol using rANS.
+// cum_prob: The cumulative probability before this symbol (the offset of
+// the symbol in the symbol cycle)
+// prob: The probability of this symbol (l_s from the paper)
+// RANS_PRECISION takes the place of m from the paper.
+static INLINE void rans_write(struct AnsCoder *ans, aom_cdf_prob cum_prob,
+ aom_cdf_prob prob) {
+ unsigned quotient, remainder;
+ while (ans->state >= L_BASE / RANS_PRECISION * IO_BASE * prob) {
ans->buf[ans->buf_offset++] = ans->state % IO_BASE;
ans->state /= IO_BASE;
}
- ANS_DIVREM(quot, rem, ans->state, p);
- ans->state = quot * RANS_PRECISION + rem + sym->cum_prob;
+ ANS_DIVREM(quotient, remainder, ans->state, prob);
+ ans->state = quotient * RANS_PRECISION + remainder + cum_prob;
}
#undef ANS_DIV8
