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120 lines
2.8 KiB
120 lines
2.8 KiB
#ifndef INCLUDED_tlsfbits
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#define INCLUDED_tlsfbits
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#if defined(__cplusplus)
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#define tlsf_decl inline
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#else
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#define tlsf_decl static
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#endif
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/*
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** Architecture-specific bit manipulation routines.
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**
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** TLSF achieves O(1) cost for malloc and free operations by limiting
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** the search for a free block to a free list of guaranteed size
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** adequate to fulfill the request, combined with efficient free list
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** queries using bitmasks and architecture-specific bit-manipulation
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** routines.
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**
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** Most modern processors provide instructions to count leading zeroes
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** in a word, find the lowest and highest set bit, etc. These
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** specific implementations will be used when available, falling back
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** to a reasonably efficient generic implementation.
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**
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** NOTE: TLSF spec relies on ffs/fls returning value 0..31.
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** ffs/fls return 1-32 by default, returning 0 for error.
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*/
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/*
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** Detect whether or not we are building for a 32- or 64-bit (LP/LLP)
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** architecture. There is no reliable portable method at compile-time.
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*/
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#if defined (__alpha__) || defined (__ia64__) || defined (__x86_64__) \
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|| defined (_WIN64) || defined (__LP64__) || defined (__LLP64__)
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#define TLSF_64BIT
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#endif
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/*
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** gcc 3.4 and above have builtin support, specialized for architecture.
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** Some compilers masquerade as gcc; patchlevel test filters them out.
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**
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** Note: clang is compatible with GCC builtins and will also define those macros
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*/
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#if defined (__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)) \
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&& defined (__GNUC_PATCHLEVEL__)
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tlsf_decl int tlsf_ffs(unsigned int word)
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{
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return __builtin_ffs(word) - 1;
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}
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tlsf_decl int tlsf_fls(unsigned int word)
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{
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const int bit = word ? 32 - __builtin_clz(word) : 0;
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return bit - 1;
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}
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#if defined (TLSF_64BIT)
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tlsf_decl int tlsf_fls_sizet(size_t size)
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{
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const int bit = size ? 64 - __builtin_clzl(size) : 0;
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return bit - 1;
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}
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#endif
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#else
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/* Fall back to generic implementation. */
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tlsf_decl int tlsf_fls_generic(unsigned int word)
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{
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int bit = 32;
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if (!word) bit -= 1;
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if (!(word & 0xffff0000)) { word <<= 16; bit -= 16; }
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if (!(word & 0xff000000)) { word <<= 8; bit -= 8; }
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if (!(word & 0xf0000000)) { word <<= 4; bit -= 4; }
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if (!(word & 0xc0000000)) { word <<= 2; bit -= 2; }
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if (!(word & 0x80000000)) { word <<= 1; bit -= 1; }
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return bit;
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}
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/* Implement ffs in terms of fls. */
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tlsf_decl int tlsf_ffs(unsigned int word)
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{
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return tlsf_fls_generic(word & (~word + 1)) - 1;
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}
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tlsf_decl int tlsf_fls(unsigned int word)
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{
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return tlsf_fls_generic(word) - 1;
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}
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#if defined (TLSF_64BIT)
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tlsf_decl int tlsf_fls_sizet(size_t size)
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{
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int high = (int)(size >> 32);
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int bits = 0;
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if (high)
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{
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bits = 32 + tlsf_fls(high);
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}
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else
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{
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bits = tlsf_fls((int)size & 0xffffffff);
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}
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return bits;
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}
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#endif /* defined (TLSF_64BIT) */
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#endif /* GNUC */
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#if !defined (TLSF_64BIT)
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#define tlsf_fls_sizet tlsf_fls
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#endif
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#undef tlsf_decl
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#endif
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