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/*
* 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