Reorder the members of TokenExtra structure
The members of TokenExtra structure, token and color_ctx, are reordered
to improve the performance of read and write operations.
BUG=aomedia:2970
Change-Id: Idff045c88cc5486339acc8ca0a71256a81236375
diff --git a/av1/encoder/tokenize.h b/av1/encoder/tokenize.h
index ddd5525..51eb28c 100644
--- a/av1/encoder/tokenize.h
+++ b/av1/encoder/tokenize.h
@@ -20,18 +20,29 @@
extern "C" {
#endif
-// The color_ctx and token members of the TokenExtra structure are used
-// to store index of the color context and color index of each pixel in
+// The token and color_ctx members of the TokenExtra structure are used
+// to store the indices of color and color context of each pixel in
// case of palette mode.
-// 1) color_ctx can take 5 (PALETTE_COLOR_INDEX_CONTEXTS) valid values, i.e.,
+// 1) token can take values in the range of [0, 7] as maximum number of possible
+// colors is 8 (PALETTE_COLORS). Hence token requires 3 bits (unsigned).
+// 2) The reserved field (1-bit) is positioned such that color_ctx occupies the
+// most significant bits and token occupies the least significant bits of the
+// byte. Thus accesses to token and color_ctx are optimal. If TokenExtra is
+// defined as:
+// typedef struct {
+// int8_t color_ctx : 4;
+// uint8_t token : 3;
+// } TokenExtra;
+// then read of color_ctx requires an extra left shift to facilitate sign
+// extension and write of token requires an extra masking.
+// 3) color_ctx can take 5 (PALETTE_COLOR_INDEX_CONTEXTS) valid values, i.e.,
// from 0 to 4. As per the current implementation it can take values in the
// range of [-1, 4]. Here -1 corresponds to invalid color index context and is
// used for default initialization. Hence color_ctx requires 4 bits (signed).
-// 2) token can take values in the range of [0, 7] as maximum number of possible
-// colors is 8 (PALETTE_COLORS). Hence token requires 3 bits (unsigned).
typedef struct {
- int8_t color_ctx : 4;
uint8_t token : 3;
+ uint8_t reserved : 1;
+ int8_t color_ctx : 4;
} TokenExtra;
typedef struct {
