Return 1+index of the first set bit in w; return 0 if w == 0.
| 34 | |
| 35 | // Return 1+index of the first set bit in w; return 0 if w == 0. |
| 36 | static size_t FindFirstSet(uint32 w) { |
| 37 | // TODO(jeff,sanjay): If this becomes a performance issue, we could |
| 38 | // use the __builtin_ffs(w) routine on GCC, or the ffs(w) routine on |
| 39 | // some other platforms. |
| 40 | |
| 41 | // clang-format off |
| 42 | static uint8 kLowestBitSet[256] = { |
| 43 | /* 0*/ 0, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 44 | /* 16*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 45 | /* 32*/ 6, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 46 | /* 48*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 47 | /* 64*/ 7, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 48 | /* 80*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 49 | /* 96*/ 6, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 50 | /*112*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 51 | /*128*/ 8, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 52 | /*144*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 53 | /*160*/ 6, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 54 | /*176*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 55 | /*192*/ 7, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 56 | /*208*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 57 | /*224*/ 6, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 58 | /*240*/ 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, |
| 59 | }; |
| 60 | // clang-format on |
| 61 | if (w & 0xff) { |
| 62 | return kLowestBitSet[w & 0xff]; |
| 63 | } else if ((w >> 8) & 0xff) { |
| 64 | return kLowestBitSet[(w >> 8) & 0xff] + 8; |
| 65 | } else if ((w >> 16) & 0xff) { |
| 66 | return kLowestBitSet[(w >> 16) & 0xff] + 16; |
| 67 | } else if ((w >> 24) & 0xff) { |
| 68 | return kLowestBitSet[(w >> 24) & 0xff] + 24; |
| 69 | } else { |
| 70 | return 0; |
| 71 | } |
| 72 | } |
| 73 | |
| 74 | size_t Bitmap::FirstUnset(size_t start) const { |
| 75 | if (start >= nbits_) { |