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Add support for BITS=24 case

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The main advantage is that you can avoid the use of uint64_t
some times, sticking to 32bit only.
Default still is BITS=32, this is mainly "in case".

Change-Id: Id694028793117ba822c37d46ef6c52fa0afed4ac
This commit is contained in:
skal 2012-11-26 23:47:08 +01:00
parent 2e7f6e8ef2
commit ba2aa0fdda
1 changed files with 11 additions and 4 deletions
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15
src/utils/bit_reader.h
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@ -25,7 +25,8 @@ extern "C" {
#endif
//------------------------------------------------------------------------------
// BITS can be either 32, 16 or 8. Pick values that fit natural register size.
// BITS can be either 32, 24, 16 or 8.
// Pick values that fit natural register size.
#if defined(__i386__) || defined(_M_IX86) // x86 32bit
#define BITS 16
@ -42,6 +43,9 @@ extern "C" {
#if (BITS == 32)
typedef uint64_t bit_t; // natural register type
typedef uint32_t lbit_t; // natural type for memory I/O
#elif (BITS == 24)
typedef uint32_t bit_t;
typedef uint32_t lbit_t;
#elif (BITS == 16)
typedef uint32_t bit_t;
typedef uint16_t lbit_t;
@ -93,23 +97,26 @@ static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
lbit_t in_bits = *(lbit_t*)br->buf_;
br->buf_ += (BITS) >> 3;
#if !defined(__BIG_ENDIAN__)
#if (BITS == 32)
#if (BITS == 32) || (BITS == 24)
#if defined(__i386__) || defined(__x86_64__)
__asm__ volatile("bswap %k0" : "=r"(in_bits) : "0"(in_bits));
bits = (bit_t)in_bits; // 32b -> 64b zero-extension
bits = (bit_t)in_bits; // 24b/32b -> 32b/64b zero-extension
#elif defined(_MSC_VER)
bits = _byteswap_ulong(in_bits);
#else
bits = (bit_t)(in_bits >> 24) | ((in_bits >> 8) & 0xff00)
| ((in_bits << 8) & 0xff0000) | (in_bits << 24);
#endif // x86
#if (BITS == 24)
bits >>= 8;
#endif
#elif (BITS == 16)
// gcc will recognize a 'rorw $8, ...' here:
bits = (bit_t)(in_bits >> 8) | ((in_bits & 0xff) << 8);
#else // BITS == 8
bits = (bit_t)in_bits;
#endif
#else // LITTLE_ENDIAN
#else // BIG_ENDIAN
bits = (bit_t)in_bits;
#endif
br->value_ |= bits << br->missing_;