From f591ef48f887f6c1608cdd89d78eebacd27e8552 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Fri, 3 Oct 2014 00:15:00 +1000 Subject: [PATCH] bitmap: Implement bitmap_ffs() This adds a bitmap_ffs() function to find the first (by the usual bitmap bit ordering) 1 bit in a bitmap between two given bits. Signed-off-by: David Gibson Signed-off-by: Rusty Russell --- ccan/bitmap/bitmap.c | 65 +++++++++++++++++++++++++++++++++ ccan/bitmap/bitmap.h | 3 ++ ccan/bitmap/test/run-ffs.c | 74 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 142 insertions(+) create mode 100644 ccan/bitmap/test/run-ffs.c diff --git a/ccan/bitmap/bitmap.c b/ccan/bitmap/bitmap.c index a6058117..d812af6a 100644 --- a/ccan/bitmap/bitmap.c +++ b/ccan/bitmap/bitmap.c @@ -58,3 +58,68 @@ void bitmap_fill_range(bitmap *bitmap, unsigned long n, unsigned long m) if (m > am) BITMAP_WORD(bitmap, m) |= bitmap_bswap(tailmask); } + +static int bitmap_clz(bitmap_word w) +{ +#if HAVE_BUILTIN_CLZL + return __builtin_clzl(w); +#else + int lz = 0; + bitmap_word mask = 1UL << (BITMAP_WORD_BITS - 1); + + while (!(w & mask)) { + lz++; + mask >>= 1; + } + + return lz; +#endif +} + +unsigned long bitmap_ffs(const bitmap *bitmap, + unsigned long n, unsigned long m) +{ + unsigned long an = BIT_ALIGN_UP(n); + unsigned long am = BIT_ALIGN_DOWN(m); + bitmap_word headmask = -1ULL >> (n % BITMAP_WORD_BITS); + bitmap_word tailmask = ~(-1ULL >> (m % BITMAP_WORD_BITS)); + + assert(m >= n); + + if (am < an) { + bitmap_word w = bitmap_bswap(BITMAP_WORD(bitmap, n)); + + w &= (headmask & tailmask); + + return w ? am + bitmap_clz(w) : m; + } + + if (an > n) { + bitmap_word w = bitmap_bswap(BITMAP_WORD(bitmap, n)); + + w &= headmask; + + if (w) + return BIT_ALIGN_DOWN(n) + bitmap_clz(w); + } + + while (an < am) { + bitmap_word w = bitmap_bswap(BITMAP_WORD(bitmap, an)); + + if (w) + return an + bitmap_clz(w); + + an += BITMAP_WORD_BITS; + } + + if (m > am) { + bitmap_word w = bitmap_bswap(BITMAP_WORD(bitmap, m)); + + w &= tailmask; + + if (w) + return am + bitmap_clz(w); + } + + return m; +} diff --git a/ccan/bitmap/bitmap.h b/ccan/bitmap/bitmap.h index 6c8d7e4d..6cbf9a22 100644 --- a/ccan/bitmap/bitmap.h +++ b/ccan/bitmap/bitmap.h @@ -187,6 +187,9 @@ static inline bool bitmap_empty(const bitmap *bitmap, unsigned long nbits) return true; } +unsigned long bitmap_ffs(const bitmap *bitmap, + unsigned long n, unsigned long m); + /* * Allocation functions */ diff --git a/ccan/bitmap/test/run-ffs.c b/ccan/bitmap/test/run-ffs.c new file mode 100644 index 00000000..0f6cc4cf --- /dev/null +++ b/ccan/bitmap/test/run-ffs.c @@ -0,0 +1,74 @@ +#include +#include +#include +#include + +#include + +int bitmap_sizes[] = { + 1, 2, 3, 4, 5, 6, 7, 8, + 16, 17, 24, 32, 33, + 64, 65, 127, 128, 129, + 1023, 1024, 1025, +}; +#define NSIZES ARRAY_SIZE(bitmap_sizes) + +#define ok_eq(a, b) \ + ok((a) == (b), "%s [%u] == %s [%u]", \ + #a, (unsigned)(a), #b, (unsigned)(b)) + +static void test_size(int nbits) +{ + BITMAP_DECLARE(bitmap, nbits); + int i; + + bitmap_zero(bitmap, nbits); + ok_eq(bitmap_ffs(bitmap, 0, nbits), nbits); + + for (i = 0; i < nbits; i++) { + bitmap_zero(bitmap, nbits); + bitmap_set_bit(bitmap, i); + + ok_eq(bitmap_ffs(bitmap, 0, nbits), i); + ok_eq(bitmap_ffs(bitmap, i, nbits), i); + ok_eq(bitmap_ffs(bitmap, i + 1, nbits), nbits); + + bitmap_zero(bitmap, nbits); + bitmap_fill_range(bitmap, i, nbits); + + ok_eq(bitmap_ffs(bitmap, 0, nbits), i); + ok_eq(bitmap_ffs(bitmap, i, nbits), i); + ok_eq(bitmap_ffs(bitmap, i + 1, nbits), (i + 1)); + ok_eq(bitmap_ffs(bitmap, nbits - 1, nbits), (nbits - 1)); + + if (i > 0) { + ok_eq(bitmap_ffs(bitmap, 0, i), i); + ok_eq(bitmap_ffs(bitmap, 0, i - 1), (i - 1)); + } + + if (i > 0) { + bitmap_zero(bitmap, nbits); + bitmap_fill_range(bitmap, 0, i); + + ok_eq(bitmap_ffs(bitmap, 0, nbits), 0); + ok_eq(bitmap_ffs(bitmap, i - 1, nbits), (i - 1)); + ok_eq(bitmap_ffs(bitmap, i, nbits), nbits); + } + } +} + +int main(void) +{ + int i; + + /* Too complicated to work out the exact number */ + plan_no_plan(); + + for (i = 0; i < NSIZES; i++) { + diag("Testing %d-bit bitmap", bitmap_sizes[i]); + test_size(bitmap_sizes[i]); + } + + /* This exits depending on whether all tests passed */ + return exit_status(); +} -- 2.39.2