| /* |
| * Copyright (C) 2014, 2021, 2024, D. R. Commander. |
| * Copyright (C) 2014, Olle Liljenzin. |
| * Copyright (C) 2020, Arm Limited. |
| * |
| * For conditions of distribution and use, see the accompanying README.ijg |
| * file. |
| */ |
| |
| /* |
| * NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be |
| * used for bit counting rather than the lookup table. This will reduce the |
| * memory footprint by 64k, which is important for some mobile applications |
| * that create many isolated instances of libjpeg-turbo (web browsers, for |
| * instance.) This may improve performance on some mobile platforms as well. |
| * This feature is enabled by default only on Arm processors, because some x86 |
| * chips have a slow implementation of bsr, and the use of clz/bsr cannot be |
| * shown to have a significant performance impact even on the x86 chips that |
| * have a fast implementation of it. When building for Armv6, you can |
| * explicitly disable the use of clz/bsr by adding -mthumb to the compiler |
| * flags (this defines __thumb__). |
| */ |
| |
| /* NOTE: Both GCC and Clang define __GNUC__ */ |
| #if (defined(__GNUC__) && (defined(__arm__) || defined(__aarch64__))) || \ |
| defined(_M_ARM) || defined(_M_ARM64) |
| #if !defined(__thumb__) || defined(__thumb2__) |
| #define USE_CLZ_INTRINSIC |
| #endif |
| #endif |
| |
| #ifdef USE_CLZ_INTRINSIC |
| #if defined(_MSC_VER) && !defined(__clang__) |
| #define JPEG_NBITS_NONZERO(x) (32 - _CountLeadingZeros(x)) |
| #else |
| #define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x)) |
| #endif |
| #define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0) |
| #else |
| extern const unsigned char jpeg_nbits_table[65536]; |
| #define JPEG_NBITS(x) (jpeg_nbits_table[x]) |
| #define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x) |
| #endif |
