Add some ANS helpers needed to replace the vpx bool coder with pure ANS.

Change-Id: I32b63fca020c410cef16e93379b4e6e281ccbccd

vp10/common/ans.h

@@ -230,6 +230,18 @@ static INLINE int uabs_read_bit(struct AnsDecoder *ans) {
   return s;
 }
 
+static INLINE int uabs_read_literal(struct AnsDecoder *ans, int bits) {
+  int literal = 0, bit;
+  assert(bits < 31);
+
+  // TODO(aconverse): Investigate ways to read/write literals faster,
+  // e.g. 8-bit chunks.
+  for (bit = bits - 1; bit >= 0; bit--)
+    literal |= uabs_read_bit(ans) << bit;
+
+  return literal;
+}
+
 struct rans_sym {
   AnsP8 prob;
   AnsP8 cum_prob;  // not-inclusive
@@ -327,6 +339,10 @@ static INLINE int ans_read_init(struct AnsDecoder *const ans,
 static INLINE int ans_read_end(struct AnsDecoder *const ans) {
   return ans->state == l_base;
 }
+
+static INLINE int ans_reader_has_error(const struct AnsDecoder *const ans) {
+  return ans->state < l_base && ans->buf_offset == 0;
+}
 #undef ANS_DIVREM
 #ifdef __cplusplus
 }  // extern "C"

vp10/encoder/buf_ans.h

@@ -81,6 +81,18 @@ static INLINE void buf_ans_flush(const struct BufAnsCoder *const c,
   }
 }
 
+static INLINE void buf_uabs_write_bit(struct BufAnsCoder *c, int bit) {
+  buf_uabs_write(c, bit, 128);
+}
+
+static INLINE void buf_uabs_write_literal(struct BufAnsCoder *c,
+                                          int literal, int bits) {
+  int bit;
+
+  assert(bits < 31);
+  for (bit = bits - 1; bit >= 0; bit--)
+    buf_uabs_write_bit(c, 1 & (literal >> bit));
+}
 #ifdef __cplusplus
 }  // extern "C"
 #endif  // __cplusplus