[FFmpeg-devel] [PATCHv5 1/4] lavc/h263dsp: add DCT dequantisation functions

[Rémi Denis-Courmont]

Note that optimised implementations of these functions will be taken
into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
are *not* overloaded by existing optimisations.

---
This adds the plus ones back, saving two branch instructions in C and
one in assembler (at the cost of two unconditional adds).

---
 libavcodec/h263dsp.c | 26 ++++++++++++++++++++++++++
 libavcodec/h263dsp.h |  4 ++++
 2 files changed, 30 insertions(+)

diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
index 6a13353499..f4523a68c1 100644
--- a/libavcodec/h263dsp.c
+++ b/libavcodec/h263dsp.c
@@ -19,10 +19,34 @@
 #include <stdint.h>
 
 #include "libavutil/attributes.h"
+#include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "config.h"
 #include "h263dsp.h"
 
+static void h263_dct_unquantize_inter_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    for (size_t i = 0; i < len; i++) {
+        int level = block[i];
+
+        if (level) {
+            if (level < 0)
+                level = level * qmul - qadd;
+            else
+                level = level * qmul + qadd;
+            block[i] = level;
+        }
+    }
+}
+
+static void h263_dct_unquantize_intra_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    av_assert1(len >= 1);
+    h263_dct_unquantize_inter_c(block + 1, len - 1, qmul, qadd);
+}
+
 const uint8_t ff_h263_loop_filter_strength[32] = {
     0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
     7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
@@ -116,6 +140,8 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
 
 av_cold void ff_h263dsp_init(H263DSPContext *ctx)
 {
+    ctx->h263_dct_unquantize_intra = h263_dct_unquantize_intra_c;
+    ctx->h263_dct_unquantize_inter = h263_dct_unquantize_inter_c;
     ctx->h263_h_loop_filter = h263_h_loop_filter_c;
     ctx->h263_v_loop_filter = h263_v_loop_filter_c;
 
diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
index 2dccd23392..0ecbe83314 100644
--- a/libavcodec/h263dsp.h
+++ b/libavcodec/h263dsp.h
@@ -24,6 +24,10 @@
 extern const uint8_t ff_h263_loop_filter_strength[32];
 
 typedef struct H263DSPContext {
+    void (*h263_dct_unquantize_intra)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
+    void (*h263_dct_unquantize_inter)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
     void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
     void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
 } H263DSPContext;
-- 
2.45.1