/* * BIRD Library -- Generic Bit Operations * * (c) 1998 Martin Mares * * Can be freely distributed and used under the terms of the GNU GPL. */ #include "nest/bird.h" #include "bitops.h" /** * u32_mkmask - create a bit mask * @n: number of bits * * u32_mkmask() returns an unsigned 32-bit integer which binary * representation consists of @n ones followed by zeroes. */ u32 u32_mkmask(uint n) { return n ? ~((1 << (32 - n)) - 1) : 0; } /** * u32_masklen - calculate length of a bit mask * @x: bit mask * * This function checks whether the given integer @x represents * a valid bit mask (binary representation contains first ones, then * zeroes) and returns the number of ones or 255 if the mask is invalid. */ uint u32_masklen(u32 x) { int l = 0; u32 n = ~x; if (n & (n+1)) return 255; if (x & 0x0000ffff) { x &= 0x0000ffff; l += 16; } if (x & 0x00ff00ff) { x &= 0x00ff00ff; l += 8; } if (x & 0x0f0f0f0f) { x &= 0x0f0f0f0f; l += 4; } if (x & 0x33333333) { x &= 0x33333333; l += 2; } if (x & 0x55555555) l++; if (x & 0xaaaaaaaa) l++; return l; } /** * u32_log2 - compute a binary logarithm. * @v: number * * This function computes a integral part of binary logarithm of given * integer @v and returns it. The computed value is also an index of the * most significant non-zero bit position. */ u32 u32_log2(u32 v) { /* The code from http://www-graphics.stanford.edu/~seander/bithacks.html */ u32 r, shift; r = (v > 0xFFFF) << 4; v >>= r; shift = (v > 0xFF ) << 3; v >>= shift; r |= shift; shift = (v > 0xF ) << 2; v >>= shift; r |= shift; shift = (v > 0x3 ) << 1; v >>= shift; r |= shift; r |= (v >> 1); return r; }