+static void fill16(uint8_t *dst, int len)
+{
+ uint32_t v = AV_RN16(dst - 2);
+
+ v |= v << 16;
+
+ while (len >= 4) {
+ AV_WN32(dst, v);
+ dst += 4;
+ len -= 4;
+ }
+
+ while (len--) {
+ *dst = dst[-2];
+ dst++;
+ }
+}
+
+static void fill24(uint8_t *dst, int len)
+{
+#if HAVE_BIGENDIAN
+ uint32_t v = AV_RB24(dst - 3);
+ uint32_t a = v << 8 | v >> 16;
+ uint32_t b = v << 16 | v >> 8;
+ uint32_t c = v << 24 | v;
+#else
+ uint32_t v = AV_RL24(dst - 3);
+ uint32_t a = v | v << 24;
+ uint32_t b = v >> 8 | v << 16;
+ uint32_t c = v >> 16 | v << 8;
+#endif
+
+ while (len >= 12) {
+ AV_WN32(dst, a);
+ AV_WN32(dst + 4, b);
+ AV_WN32(dst + 8, c);
+ dst += 12;
+ len -= 12;
+ }
+
+ if (len >= 4) {
+ AV_WN32(dst, a);
+ dst += 4;
+ len -= 4;
+ }
+
+ if (len >= 4) {
+ AV_WN32(dst, b);
+ dst += 4;
+ len -= 4;
+ }
+
+ while (len--) {
+ *dst = dst[-3];
+ dst++;
+ }
+}
+
+static void fill32(uint8_t *dst, int len)
+{
+ uint32_t v = AV_RN32(dst - 4);
+
+ while (len >= 4) {
+ AV_WN32(dst, v);
+ dst += 4;
+ len -= 4;
+ }
+
+ while (len--) {
+ *dst = dst[-4];
+ dst++;
+ }
+}
+
+void av_memcpy_backptr(uint8_t *dst, int back, int cnt)
+{
+ const uint8_t *src = &dst[-back];
+ if (back == 1) {
+ memset(dst, *src, cnt);
+ } else if (back == 2) {
+ fill16(dst, cnt);
+ } else if (back == 3) {
+ fill24(dst, cnt);
+ } else if (back == 4) {
+ fill32(dst, cnt);
+ } else {
+ if (cnt >= 16) {
+ int blocklen = back;
+ while (cnt > blocklen) {
+ memcpy(dst, src, blocklen);
+ dst += blocklen;
+ cnt -= blocklen;
+ blocklen <<= 1;
+ }
+ memcpy(dst, src, cnt);
+ return;
+ }
+ if (cnt >= 8) {
+ AV_COPY32U(dst, src);
+ AV_COPY32U(dst + 4, src + 4);
+ src += 8;
+ dst += 8;
+ cnt -= 8;
+ }
+ if (cnt >= 4) {
+ AV_COPY32U(dst, src);
+ src += 4;
+ dst += 4;
+ cnt -= 4;
+ }
+ if (cnt >= 2) {
+ AV_COPY16U(dst, src);
+ src += 2;
+ dst += 2;
+ cnt -= 2;
+ }
+ if (cnt)
+ *dst = *src;
+ }
+}