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
diff --git a/aom_dsp/bitwriter.h b/aom_dsp/bitwriter.h
index d288393..57f08db 100644
--- a/aom_dsp/bitwriter.h
+++ b/aom_dsp/bitwriter.h
@@ -186,12 +186,11 @@
static INLINE void aom_write_cdf(aom_writer *w, int symb,
const aom_cdf_prob *cdf, int nsymbs) {
#if CONFIG_ANS
- struct rans_sym s;
(void)nsymbs;
assert(cdf);
- s.cum_prob = symb > 0 ? cdf[symb - 1] : 0;
- s.prob = cdf[symb] - s.cum_prob;
- buf_rans_write(w, &s);
+ const aom_cdf_prob cum_prob = symb > 0 ? cdf[symb - 1] : 0;
+ const aom_cdf_prob prob = cdf[symb] - cum_prob;
+ buf_rans_write(w, cum_prob, prob);
#elif CONFIG_DAALA_EC
daala_write_symbol(w, symb, cdf, nsymbs);
#else
diff --git a/aom_dsp/buf_ans.c b/aom_dsp/buf_ans.c
index 80948cc..8fe1ff7 100644
--- a/aom_dsp/buf_ans.c
+++ b/aom_dsp/buf_ans.c
@@ -60,10 +60,7 @@
}
for (offset = offset - 1; offset >= 0; --offset) {
if (c->buf[offset].method == ANS_METHOD_RANS) {
- struct rans_sym sym;
- sym.prob = c->buf[offset].prob;
- sym.cum_prob = c->buf[offset].val_start;
- rans_write(&c->ans, &sym);
+ rans_write(&c->ans, c->buf[offset].val_start, c->buf[offset].prob);
} else {
rabs_write(&c->ans, (uint8_t)c->buf[offset].val_start,
(AnsP8)c->buf[offset].prob);
diff --git a/aom_dsp/buf_ans.h b/aom_dsp/buf_ans.h
index 90f36a2..0768506 100644
--- a/aom_dsp/buf_ans.h
+++ b/aom_dsp/buf_ans.h
@@ -88,8 +88,13 @@
#endif
}
+// Buffer one symbol for encoding 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 buf_rans_write(struct BufAnsCoder *const c,
- const struct rans_sym *const sym) {
+ aom_cdf_prob cum_prob, aom_cdf_prob prob) {
assert(c->offset <= c->size);
#if !ANS_MAX_SYMBOLS
if (c->offset == c->size) {
@@ -97,8 +102,8 @@
}
#endif
c->buf[c->offset].method = ANS_METHOD_RANS;
- c->buf[c->offset].val_start = sym->cum_prob;
- c->buf[c->offset].prob = sym->prob;
+ c->buf[c->offset].val_start = cum_prob;
+ c->buf[c->offset].prob = prob;
++c->offset;
#if ANS_MAX_SYMBOLS
if (c->offset == c->size) aom_buf_ans_flush(c);
diff --git a/test/ans_test.cc b/test/ans_test.cc
index 2e513ea..a553a9e 100644
--- a/test/ans_test.cc
+++ b/test/ans_test.cc
@@ -87,6 +87,11 @@
const int kRansSymbols =
static_cast<int>(sizeof(spareto65) / sizeof(spareto65[0]));
+struct rans_sym {
+ aom_cdf_prob prob;
+ aom_cdf_prob cum_prob; // not-inclusive
+};
+
std::vector<int> ans_encode_build_vals(rans_sym *const tab, int iters) {
aom_cdf_prob sum = 0;
for (int i = 0; i < kRansSymbols; ++i) {
@@ -128,7 +133,7 @@
std::clock_t start = std::clock();
for (std::vector<int>::const_iterator it = sym_vec.begin();
it != sym_vec.end(); ++it) {
- buf_rans_write(&a, &tab[*it]);
+ buf_rans_write(&a, tab[*it].cum_prob, tab[*it].prob);
}
aom_buf_ans_flush(&a);
std::clock_t enc_time = std::clock() - start;
