diff options
Diffstat (limited to 'ch2/2-09_bitcount.c')
| -rw-r--r-- | ch2/2-09_bitcount.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/ch2/2-09_bitcount.c b/ch2/2-09_bitcount.c index d824ca6..6ad6086 100644 --- a/ch2/2-09_bitcount.c +++ b/ch2/2-09_bitcount.c @@ -7,7 +7,7 @@ * faster version of bitcount. * * Answer: Subtracting 1 from a number reverses the rightmost 1 bit and - * replaces all lower-order bits to 0. So for example: + * replaces all lower-order bits to 1. So for example: * * 110100 (52) minus 1 is * 110011 (51) @@ -22,6 +22,18 @@ * Why? Because the 2nd operand (51) is only masking off two fields, the 3rd * and 4th (which are zeros). The rightmost 1-bit in the 1st operand (52) is * in that mask, so it goes poof. + * + * Oh, and here's the in-book version of bitcount(): + * + * int bitcount(unsigned x) { + * int b; + * for (b = 0; x != 0; x >>= 1) { + * if (x & 01) { + * b++; + * } + * } + * return b; + * } */ unsigned bitcount(unsigned x) { |