ans: Use a fixed N-symbol window
Accept a small compression loss is in exchange for a fixed sized encoder
side buffering requirement.
subset1:
rans_base@2016-12-02T22:55:56.809Z -> rans_nsym@2016-12-02T22:58:19.859Z
PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM | CIEDE 2000
0.0304 | 0.0303 | 0.0305 | 0.0317 | 0.0312 | 0.0309 | 0.0301
Change-Id: I09dd143e4f1638b97dc9bba7023efa837a7d48c7
diff --git a/aom_dsp/ans.h b/aom_dsp/ans.h
index f84671c..8a30c9b 100644
--- a/aom_dsp/ans.h
+++ b/aom_dsp/ans.h
@@ -23,7 +23,8 @@
extern "C" {
#endif // __cplusplus
-#define ANS_REVERSE 0
+#define ANS_MAX_SYMBOLS (1 << 24)
+#define ANS_REVERSE 1
typedef uint8_t AnsP8;
#define ANS_P8_PRECISION 256u
diff --git a/aom_dsp/ansreader.h b/aom_dsp/ansreader.h
index e0b02f7..8a7788e 100644
--- a/aom_dsp/ansreader.h
+++ b/aom_dsp/ansreader.h
@@ -32,11 +32,16 @@
const uint8_t *buf;
int buf_offset;
uint32_t state;
+#if ANS_MAX_SYMBOLS
+ int symbols_left;
+#endif
#if CONFIG_ACCOUNTING
Accounting *accounting;
#endif
};
+static INLINE int ans_read_reinit(struct AnsDecoder *const ans);
+
static INLINE unsigned refill_state(struct AnsDecoder *const ans,
unsigned state) {
#if ANS_REVERSE
@@ -55,7 +60,14 @@
AnsP8 p = ANS_P8_PRECISION - p0;
int s;
unsigned xp, sp;
- unsigned state = ans->state;
+ unsigned state;
+#if ANS_MAX_SYMBOLS
+ if (ans->symbols_left-- == 0) {
+ ans_read_reinit(ans);
+ ans->symbols_left--;
+ }
+#endif
+ state = ans->state;
sp = state * p;
xp = sp / ANS_P8_PRECISION;
s = (sp & 0xFF) >= p0;
@@ -69,7 +81,14 @@
static INLINE int uabs_read_bit(struct AnsDecoder *ans) {
int s;
- unsigned state = ans->state;
+ unsigned state;
+#if ANS_MAX_SYMBOLS
+ if (ans->symbols_left-- == 0) {
+ ans_read_reinit(ans);
+ ans->symbols_left--;
+ }
+#endif
+ state = ans->state;
s = (int)(state & 1);
state >>= 1;
ans->state = refill_state(ans, state);
@@ -100,6 +119,12 @@
unsigned rem;
unsigned quo;
struct rans_dec_sym sym;
+#if ANS_MAX_SYMBOLS
+ if (ans->symbols_left-- == 0) {
+ ans_read_reinit(ans);
+ ans->symbols_left--;
+ }
+#endif
quo = ans->state / RANS_PRECISION;
rem = ans->state % RANS_PRECISION;
fetch_sym(&sym, tab, rem);
@@ -150,9 +175,18 @@
#endif
ans->state += L_BASE;
if (ans->state >= L_BASE * IO_BASE) return 1;
+#if ANS_MAX_SYMBOLS
+ ans->symbols_left = ANS_MAX_SYMBOLS;
+#endif
return 0;
}
+#if ANS_REVERSE
+static INLINE int ans_read_reinit(struct AnsDecoder *const ans) {
+ return ans_read_init(ans, ans->buf + ans->buf_offset, -ans->buf_offset);
+}
+#endif
+
static INLINE int ans_read_end(struct AnsDecoder *const ans) {
return ans->state == L_BASE;
}
diff --git a/aom_dsp/answriter.h b/aom_dsp/answriter.h
index b6ac6de..220ffb1 100644
--- a/aom_dsp/answriter.h
+++ b/aom_dsp/answriter.h
@@ -89,6 +89,9 @@
ans->buf[i] = ans->buf[ans_size - 1 - i];
ans->buf[ans_size - 1 - i] = tmp;
}
+ ans->buf += ans_size;
+ ans->buf_offset = 0;
+ ans->state = L_BASE;
}
#endif
return ans_size;
diff --git a/aom_dsp/buf_ans.c b/aom_dsp/buf_ans.c
index 33db080..c4ac643 100644
--- a/aom_dsp/buf_ans.c
+++ b/aom_dsp/buf_ans.c
@@ -43,6 +43,10 @@
void aom_buf_ans_flush(struct BufAnsCoder *const c) {
int offset;
+#if ANS_MAX_SYMBOLS
+ if (c->offset == 0) return;
+#endif
+ assert(c->offset > 0);
for (offset = c->offset - 1; offset >= 0; --offset) {
if (c->buf[offset].method == ANS_METHOD_RANS) {
struct rans_sym sym;
diff --git a/aom_dsp/buf_ans.h b/aom_dsp/buf_ans.h
index f670112..b315bd7 100644
--- a/aom_dsp/buf_ans.h
+++ b/aom_dsp/buf_ans.h
@@ -71,6 +71,9 @@
c->buf[c->offset].val_start = val;
c->buf[c->offset].prob = prob;
++c->offset;
+#if ANS_MAX_SYMBOLS
+ if (c->offset == ANS_MAX_SYMBOLS) aom_buf_ans_flush(c);
+#endif
}
static INLINE void buf_rans_write(struct BufAnsCoder *const c,
@@ -83,6 +86,9 @@
c->buf[c->offset].val_start = sym->cum_prob;
c->buf[c->offset].prob = sym->prob;
++c->offset;
+#if ANS_MAX_SYMBOLS
+ if (c->offset == ANS_MAX_SYMBOLS) aom_buf_ans_flush(c);
+#endif
}
static INLINE void buf_uabs_write_bit(struct BufAnsCoder *c, int bit) {
