arm: get_cabac inline asm

Based on the aarch64 asm. CPU cycle counts on cortex-a9 compared to
gcc 4.8.2:
before: 475 decicycles in get_cabac_noinline, 67106035 runs, 2829 skips
after:  393 decicycles in get_cabac_noinline, 67106474 runs, 2390 skips

Overall speedup is above 2%. Code generated by clang 3.4 is slower on
the same hardware and the relative change is a little larger.

libavcodec/arm/cabac.h

+/*
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_ARM_CABAC_H
+#define AVCODEC_ARM_CABAC_H
+
+#include "config.h"
+#if HAVE_ARMV6T2_INLINE
+
+#include "libavutil/attributes.h"
+#include "libavutil/internal.h"
+#include "libavcodec/cabac.h"
+
+#define get_cabac_inline get_cabac_inline_arm
+static av_always_inline int get_cabac_inline_arm(CABACContext *c,
+                                                 uint8_t *const state)
+{
+    int bit;
+    void *reg_b, *reg_c, *tmp;
+
+    __asm__ volatile(
+        "ldrb       %[bit]        , [%[state]]                  \n\t"
+        "add        %[r_b]        , %[tables]   , %[lps_off]    \n\t"
+        "mov        %[tmp]        , %[range]                    \n\t"
+        "and        %[range]      , %[range]    , #0xC0         \n\t"
+        "add        %[r_b]        , %[r_b]      , %[bit]        \n\t"
+        "ldrb       %[range]      , [%[r_b], %[range], lsl #1]  \n\t"
+        "add        %[r_b]        , %[tables]   , %[norm_off]   \n\t"
+        "sub        %[r_c]        , %[tmp]      , %[range]      \n\t"
+        "lsl        %[tmp]        , %[r_c]      , #17           \n\t"
+        "cmp        %[tmp]        , %[low]                      \n\t"
+        "it         gt                                          \n\t"
+        "movgt      %[range]      , %[r_c]                      \n\t"
+        "itt        cc                                          \n\t"
+        "mvncc      %[bit]        , %[bit]                      \n\t"
+        "subcc      %[low]        , %[low]      , %[tmp]        \n\t"
+        "add        %[r_c]        , %[tables]   , %[mlps_off]   \n\t"
+        "ldrb       %[tmp]        , [%[r_b], %[range]]          \n\t"
+        "ldrb       %[r_b]        , [%[r_c], %[bit]]            \n\t"
+        "lsl        %[low]        , %[low]      , %[tmp]        \n\t"
+        "lsl        %[range]      , %[range]    , %[tmp]        \n\t"
+        "uxth       %[r_c]        , %[low]                      \n\t"
+        "strb       %[r_b]        , [%[state]]                  \n\t"
+        "tst        %[r_c]        , %[r_c]                      \n\t"
+        "bne        2f                                          \n\t"
+        "ldr        %[r_c]        , [%[c], %[byte]]             \n\t"
+        "ldr        %[r_b]        , [%[c], %[end]]              \n\t"
+        "ldrh       %[tmp]        , [%[r_c]]                    \n\t"
+        "cmp        %[r_c]        , %[r_b]                      \n\t"
+        "itt        lt                                          \n\t"
+        "addlt      %[r_c]        , %[r_c]      , #2            \n\t"
+        "strlt      %[r_c]        , [%[c], %[byte]]             \n\t"
+        "sub        %[r_c]        , %[low]      , #1            \n\t"
+        "add        %[r_b]        , %[tables]   , %[norm_off]   \n\t"
+        "eor        %[r_c]        , %[low]      , %[r_c]        \n\t"
+        "rev        %[tmp]        , %[tmp]                      \n\t"
+        "lsr        %[r_c]        , %[r_c]      , #15           \n\t"
+        "lsr        %[tmp]        , %[tmp]      , #15           \n\t"
+        "ldrb       %[r_c]        , [%[r_b], %[r_c]]            \n\t"
+        "movw       %[r_b]        , #0xFFFF                     \n\t"
+        "sub        %[tmp]        , %[tmp]      , %[r_b]        \n\t"
+        "rsb        %[r_c]        , %[r_c]      , #7            \n\t"
+        "lsl        %[tmp]        , %[tmp]      , %[r_c]        \n\t"
+        "add        %[low]        , %[low]      , %[tmp]        \n\t"
+        "2:                                                     \n\t"
+        :    [bit]"=&r"(bit),
+             [low]"+&r"(c->low),
+           [range]"+&r"(c->range),
+             [r_b]"=&r"(reg_b),
+             [r_c]"=&r"(reg_c),
+             [tmp]"=&r"(tmp)
+        :        [c]"r"(c),
+             [state]"r"(state),
+            [tables]"r"(ff_h264_cabac_tables),
+              [byte]"M"(offsetof(CABACContext, bytestream)),
+               [end]"M"(offsetof(CABACContext, bytestream_end)),
+          [norm_off]"I"(H264_NORM_SHIFT_OFFSET),
+           [lps_off]"I"(H264_LPS_RANGE_OFFSET),
+          [mlps_off]"I"(H264_MLPS_STATE_OFFSET + 128)
+        : "memory", "cc"
+        );
+
+    return bit & 1;
+}
+#endif /* HAVE_ARMV6T2_INLINE */
+
+#endif /* AVCODEC_ARM_CABAC_H */

libavcodec/cabac_functions.h

@@ -35,6 +35,9 @@
 #if ARCH_AARCH64
 #   include "aarch64/cabac.h"
 #endif
+#if ARCH_ARM
+#   include "arm/cabac.h"
+#endif
 #if ARCH_X86
 #   include "x86/cabac.h"
 #endif