- 26 Mar, 2006 40 commits
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Akinobu Mita authored
<linux@horizon.com> wrote: This is an extremely well-known technique. You can see a similar version that uses a multiply for the last few steps at http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel whch refers to "Software Optimization Guide for AMD Athlon 64 and Opteron Processors" http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/25112.PDF It's section 8.6, "Efficient Implementation of Population-Count Function in 32-bit Mode", pages 179-180. It uses the name that I am more familiar with, "popcount" (population count), although "Hamming weight" also makes sense. Anyway, the proof of correctness proceeds as follows: b = a - ((a >> 1) & 0x55555555); c = (b & 0x33333333) + ((b >> 2) & 0x33333333); d = (c + (c >> 4)) & 0x0f0f0f0f; #if SLOW_MULTIPLY e = d + (d >> 8) f = e + (e >> 16); return f & 63; #else /* Useful if multiply takes at most 4 cycles */ return (d * 0x01010101) >> 24; #endif The input value a can be thought of as 32 1-bit fields each holding their own hamming weight. Now look at it as 16 2-bit fields. Each 2-bit field a1..a0 has the value 2*a1 + a0. This can be converted into the hamming weight of the 2-bit field a1+a0 by subtracting a1. That's what the (a >> 1) & mask subtraction does. Since there can be no borrows, you can just do it all at once. Enumerating the 4 possible cases: 0b00 = 0 -> 0 - 0 = 0 0b01 = 1 -> 1 - 0 = 1 0b10 = 2 -> 2 - 1 = 1 0b11 = 3 -> 3 - 1 = 2 The next step consists of breaking up b (made of 16 2-bir fields) into even and odd halves and adding them into 4-bit fields. Since the largest possible sum is 2+2 = 4, which will not fit into a 4-bit field, the 2-bit ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ "which will not fit into a 2-bit field" fields have to be masked before they are added. After this point, the masking can be delayed. Each 4-bit field holds a population count from 0..4, taking at most 3 bits. These numbers can be added without overflowing a 4-bit field, so we can compute c + (c >> 4), and only then mask off the unwanted bits. This produces d, a number of 4 8-bit fields, each in the range 0..8. From this point, we can shift and add d multiple times without overflowing an 8-bit field, and only do a final mask at the end. The number to mask with has to be at least 63 (so that 32 on't be truncated), but can also be 128 or 255. The x86 has a special encoding for signed immediate byte values -128..127, so the value of 255 is slower. On other processors, a special "sign extend byte" instruction might be faster. On a processor with fast integer multiplies (Athlon but not P4), you can reduce the final few serially dependent instructions to a single integer multiply. Consider d to be 3 8-bit values d3, d2, d1 and d0, each in the range 0..8. The multiply forms the partial products: d3 d2 d1 d0 d3 d2 d1 d0 d3 d2 d1 d0 + d3 d2 d1 d0 ---------------------- e3 e2 e1 e0 Where e3 = d3 + d2 + d1 + d0. e2, e1 and e0 obviously cannot generate any carries. Signed-off-by:
Akinobu Mita <mita@miraclelinux.com> Signed-off-by:
Andrew Morton <akpm@osdl.org> Signed-off-by:
Linus Torvalds <torvalds@osdl.org>
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Akinobu Mita authored
By defining generic hweight*() routines - hweight64() will be defined on all architectures - hweight_long() will use architecture optimized hweight32() or hweight64() I found two possible cleanups by these reasons. Signed-off-by:
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Akinobu Mita authored
generic_{ffs,fls,fls64,hweight{64,32,16,8}}() were moved into include/asm-generic/bitops.h. So all architectures don't use them. Signed-off-by: -
Akinobu Mita authored
Now the only user who are using generic_ffs() is ntfs filesystem. This patch isolates generic_ffs() as ntfs_ffs() for ntfs. Signed-off-by:
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Akinobu Mita authored
The find_*_bit() routines are defined to work on a pointer to unsigned long. But partial_page.bitmap is unsigned int and it is passed to find_*_bit() in arch/ia64/ia32/sys_ia32.c. So the compiler will print warnings. This patch changes to unsigned long instead. Signed-off-by:
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Akinobu Mita authored
The test_bit() routines are defined to work on a pointer to unsigned long. But thread_info.flags is __u32 (unsigned int) on sh and it is passed to flag set/clear/test wrappers in include/linux/thread_info.h. So the compiler will print warnings. This patch changes to unsigned long instead. Signed-off-by:
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Akinobu Mita authored
Currently include/asm-generic/bitops.h is not referenced from anywhere. But it will be the benefit of those who are trying to port Linux to another architecture. So update it by same manner Signed-off-by:
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Akinobu Mita authored
- remove {,test_and_}{set,clear,change}_bit() - remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove generic_fls64() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove generic_hweight{32,16,8}() - remove sched_find_first_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove sched_find_first_bit() - remove generic_hweight{64,32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove ffz() - remove find_{next,first}{,_zero}_bit() - remove generic_ffs() - remove generic_fls() - remove generic_fls64() - remove __ffs() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove ffz() - remove __ffs() - remove generic_fls() - remove generic_fls64() - remove sched_find_first_bit() - remove ffs() - unless defined(ULTRA_HAS_POPULATION_COUNT) - remove generic_hweight{64,32,16,8}() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove ffz() - remove __ffs() - remove sched_find_first_bit() - remove ffs() - remove generic_fls() - remove generic_fls64() - remove generic_hweight{32,16,8}() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove __ffs() - remove find_{next,first}{,_zero}_bit() - remove generic_hweight{32,16,8}() - remove sched_find_first_bit() - remove generic_ffs() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove generic_fls() - remove generic_fls64() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove find_{next,first}{,_zero}_bit() - remove generic_ffs() - remove generic_hweight{32,16,8}() - remove sched_find_first_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove generic_fls() - remove generic_fls64() Signed-off-by: -
Akinobu Mita authored
- remove generic_ffs() - remove generic_fls() - remove generic_fls64() - remove generic_hweight{64,32,16,8}() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove generic_fls64() - remove generic_hweight{64,32,16,8}() - remove sched_find_first_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove ffz() - remove generic_fls64() - remove generic_hweight{32,16,8}() - remove generic_hweight64() - remove sched_find_first_bit() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - unless defined(CONFIG_CPU_MIPS32) or defined(CONFIG_CPU_MIPS64) - remove __ffs() - remove ffs() - remove ffz() - remove fls() - remove fls64() - remove find_{next,first}{,_zero}_bit() - remove sched_find_first_bit() - remove generic_hweight64() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove ffs() - remove __ffs() - remove sched_find_first_bit() - remove ffz() - remove find_{next,first}{,_zero}_bit() - remove generic_hweight() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove generic_fls() - remove generic_fls64() Signed-off-by: -
Akinobu Mita authored
Build fix for ppc Signed-off-by:
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Akinobu Mita authored
This patch reverts ext2 bitmap functions. Signed-off-by:
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Akinobu Mita authored
- remove generic_fls64() - remove sched_find_first_bit() - remove generic_hweight() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove ffz() - remove find_{next,first}{,_zero}_bit() - remove __ffs() - remove generic_fls() - remove generic_fls64() - remove sched_find_first_bit() - remove generic_ffs() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove generic_fls64() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove sched_find_first_bit() Signed-off-by: -
Akinobu Mita authored
- remove generic_fls64() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove generic_ffs() - remove find_{next,first}{,_zero}_bit() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove ext2_{set,clear}_bit_atomic() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove generic_fls() - remove generic_fls64() Signed-off-by: -
Akinobu Mita authored
- remove ffz() - remove find_{next,first}{,_zero}_bit() - remove generic_ffs() - remove __ffs() - remove generic_fls64() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove generic_fls() - remove generic_fls64() - remove generic_hweight{32,16,8}() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() - remove sched_find_first_bit() Signed-off-by:Mikael Starvik <starvik@axis.com> Signed-off-by:
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Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - remove ffz() - remove __ffs() - remove generic_fls() - remove generic_fls64() - remove generic_ffs() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() Signed-off-by: -
Akinobu Mita authored
- remove __{,test_and_}{set,clear,change}_bit() and test_bit() - if __LINUX_ARM_ARCH__ < 5 - remove ffz() - remove __ffs() - remove generic_fls() - remove generic_ffs() - remove generic_fls64() - remove sched_find_first_bit() - remove generic_hweight{32,16,8}() Signed-off-by: -
Akinobu Mita authored
- unless defined(__alpha_cix__) and defined(__alpha_fix__) - remove generic_fls() - remove generic_hweight{64,32,16,8}() - remove generic_fls64() - remove find_{next,first}{,_zero}_bit() - remove ext2_{set,clear,test,find_first_zero,find_next_zero}_bit() - remove minix_{test,set,test_and_clear,test,find_first_zero}_bit() Signed-off-by: -
Akinobu Mita authored
This patch introduces the C-language equivalents of the functions below: int minix_test_and_set_bit(int nr, volatile unsigned long *addr); int minix_set_bit(int nr, volatile unsigned long *addr); int minix_test_and_clear_bit(int nr, volatile unsigned long *addr); int minix_test_bit(int nr, const volatile unsigned long *addr); unsigned long minix_find_first_zero_bit(const unsigned long *addr, unsigned long size); In include/asm-generic/bitops/minix.h and include/asm-generic/bitops/minix-le.h This code largely copied from: include/asm-sparc/bitops.h Signed-off-by: -
Akinobu Mita authored
This patch introduces the C-language equivalents of the functions below: int ext2_set_bit_atomic(int nr, volatile unsigned long *addr); int ext2_clear_bit_atomic(int nr, volatile unsigned long *addr); In include/asm-generic/bitops/ext2-atomic.h This code largely copied from: include/asm-sparc/bitops.h Signed-off-by:
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Akinobu Mita authored
This patch introduces the C-language equivalents of the functions below: int ext2_set_bit(int nr, volatile unsigned long *addr); int ext2_clear_bit(int nr, volatile unsigned long *addr); int ext2_test_bit(int nr, const volatile unsigned long *addr); unsigned long ext2_find_first_zero_bit(const unsigned long *addr, unsigned long size); unsinged long ext2_find_next_zero_bit(const unsigned long *addr, unsigned long size); In include/asm-generic/bitops/ext2-non-atomic.h This code largely copied from: include/asm-powerpc/bitops.h include/asm-parisc/bitops.h Signed-off-by: -
Akinobu Mita authored
Build fix for s390 declare __u32 and __u64. Signed-off-by:
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Akinobu Mita authored
This patch introduces the C-language equivalents of the functions below: unsigned int hweight32(unsigned int w); unsigned int hweight16(unsigned int w); unsigned int hweight8(unsigned int w); unsigned long hweight64(__u64 w); In include/asm-generic/bitops/hweight.h This code largely copied from: include/linux/bitops.h Signed-off-by:
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Akinobu Mita authored
This patch introduces the C-language equivalent of the function: int ffs(int x); In include/asm-generic/bitops/ffs.h This code largely copied from: include/linux/bitops.h Signed-off-by:
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Akinobu Mita authored
This patch introduces the C-language equivalent of the function: int sched_find_first_bit(const unsigned long *b); In include/asm-generic/bitops/sched.h This code largely copied from: include/asm-powerpc/bitops.h Signed-off-by:
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Akinobu Mita authored
This patch introduces the C-language equivalents of the functions below: unsigned logn find_next_bit(const unsigned long *addr, unsigned long size, unsigned long offset); unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size, unsigned long offset); unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size); unsigned long find_first_bit(const unsigned long *addr, unsigned long size); In include/asm-generic/bitops/find.h This code largely copied from: arch/powerpc/lib/bitops.c Signed-off-by: -
Akinobu Mita authored
This patch introduces the C-language equivalent of the function: int fls64(__u64 x); In include/asm-generic/bitops/fls64.h This code largely copied from: include/linux/bitops.h Signed-off-by:
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