decode: faster huffman code loading on 32-bit Arm (#703)

* platform: add macro for using the 'aligned' attribute

* decode: add accessor macros for HuffmanCode fields

Adds a constructor function for building HuffmanCode values
so they can be accessed quickly on different architectures.

Also adds macros for marking a HuffmanCode table pointer
that can be accessed quickly (BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD),
adjusting the index into that table (BROTLI_HC_ADJUST_TABLE_INDEX),
and getting the .bits or .value fields out of the table at the
current index (BROTLI_HC_GET_BITS/VALUE).

For example, assuming |table| contains a HuffmanCode pointer:

  BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD(table);
  BROTLI_HC_ADJUST_TABLE_INDEX(table, index_into_table);
  *bits = BROTLI_HC_GET_BITS(table);
  *value = BROTLI_HC_GET_VALUE(table);
  BROTLI_HC_ADJUST_TABLE_INDEX(table, offset);
  *bits2 = BROTLI_HC_GET_BITS(table);
  *value2 = BROTLI_HC_GET_VALUE(table);

All uses of the HuffmanCode have been updated appropriately.

* decode: add alternative accessors for HuffmanCode on Arm AArch32

1 files changed, 7 insertions, 1 deletions

diff --git a/c/common/platform.h b/c/common/platform.h
index 0d84b19..3945a27 100755
--- a/c/common/platform.h
+++ b/c/common/platform.h
@@ -180,6 +180,12 @@ OR:
 #define BROTLI_UNUSED_FUNCTION static BROTLI_INLINE
 #endif
 
+#if BROTLI_GNUC_HAS_ATTRIBUTE(aligned, 2, 7, 0)
+#define BROTLI_ALIGNED(N) __attribute__((aligned(N)))
+#else
+#define BROTLI_ALIGNED(N)
+#endif
+
 #if (defined(__ARM_ARCH) && (__ARM_ARCH == 7)) || \
     (defined(M_ARM) && (M_ARM == 7))
 #define BROTLI_TARGET_ARMV7
@@ -343,7 +349,7 @@ static BROTLI_INLINE void BrotliUnalignedWrite64(void* p, uint64_t v) {
 /* If __attribute__(aligned) is available, use that. Otherwise, memcpy. */
 
 #if BROTLI_GNUC_HAS_ATTRIBUTE(aligned, 2, 7, 0)
-typedef  __attribute__((aligned(1))) uint64_t brotli_unaligned_uint64_t;
+typedef BROTLI_ALIGNED(1) uint64_t brotli_unaligned_uint64_t;
 
 static BROTLI_INLINE uint64_t BrotliUnalignedRead64(const void* p) {
   return (uint64_t) ((brotli_unaligned_uint64_t*) p)[0];