diff options
Diffstat (limited to 'src/H5Tbit.c')
| -rw-r--r-- | src/H5Tbit.c | 91 |
1 files changed, 87 insertions, 4 deletions
diff --git a/src/H5Tbit.c b/src/H5Tbit.c index f3fbc3d..c986cfa 100644 --- a/src/H5Tbit.c +++ b/src/H5Tbit.c @@ -483,8 +483,8 @@ done: * Purpose: Increment part of a bit field by adding 1. The bit field * starts with bit position START and is SIZE bits long. * - * Return: Success: The carry-out value, one if overflow zero - * otherwise. + * Return: Success: The carry-out value. One if overflows, + * zero otherwise. * * Failure: Negative * @@ -547,7 +547,7 @@ H5T_bit_inc(uint8_t *buf, size_t start, size_t size) /*------------------------------------------------------------------------- - * Function: H5T_bit_dec + * Function: H5T_bit_dec2 * * Purpose: decrement part of a bit field by 1. * At this moment, START is always 0 and SIZE is a multiply @@ -564,10 +564,12 @@ H5T_bit_inc(uint8_t *buf, size_t start, size_t size) * Need to generalize it to handle random START and SIZE like * H5T_bit_inc. * + * Older algorithm. Take it out!!! + * *------------------------------------------------------------------------- */ void -H5T_bit_dec(uint8_t *buf, size_t start, size_t size) +H5T_bit_dec2(uint8_t *buf, size_t start, size_t size) { size_t idx; @@ -587,6 +589,87 @@ H5T_bit_dec(uint8_t *buf, size_t start, size_t size) /*------------------------------------------------------------------------- + * Function: H5T_bit_dec + * + * Purpose: decrement part of a bit field by substracting 1. The bit + * field starts with bit position START and is SIZE bits long. + * + * Return: Success: The "borrow-in" value. It's one if underflows, + * zero otherwise. + * + * Failure: Negative + * + * Programmer: Raymond Lu + * March 17, 2004 + * + * Modifications: + * + *------------------------------------------------------------------------- + */ +htri_t +H5T_bit_dec(uint8_t *buf, size_t start, size_t size) +{ + size_t idx = start / 8; + size_t pos = start % 8; + uint8_t tmp; + unsigned borrow = 0; + + /* Use FUNC_ENTER_NOAPI_NOINIT_NOFUNC here to avoid performance issues */ + FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5T_bit_dec); + + assert(buf); + assert(size); + + /* The first partial byte */ + if ((size+start)/8 > idx) { /*bit sequence doesn't end in the same byte as starts*/ + /* Example: a sequence like 11000100 and start = 3. We substract 00001000 from + * it and get 10111100. If a sequence is 00000111, we do right shift for START + * bits and get 00000000. So we need to borrow from higher byte when we substract + * 00001000. + */ + if(!(buf[idx] >> pos)) + borrow = 1; + buf[idx] -= 1 << pos; + idx++; + } else { /* bit sequence ends in the same byte as starts */ + /* Example: a sequence like 11000100 and start=3, size=3. We substract 00001000 + * and get 10111100. A bit is borrowed from 6th bit(buf[idx]>>6=00000010, tmp>>6=00000011, + * not equal). We need to put this bit back by increment 1000000. + */ + tmp = buf[idx]; + buf[idx] -= 1 << pos; + if((buf[idx] >> (start+size)) != tmp >> (start+size)) { + buf[idx] += 1 << (start+size); + borrow = 1; + } + goto done; + } + + /* The middle bytes */ + while (borrow && size>=8) { + if(buf[idx]) + borrow = 0; + buf[idx] -= 1; + + idx++; + size -= 8; + } + + /* The last byte */ + if (borrow && size>0) { + /* Similar to the first byte case, where sequence ends in the same byte as starts */ + tmp = buf[idx]; + buf[idx] -= 1; + if((buf[idx] >> size) != tmp >> size) + buf[idx] += 1 << size; + } + +done: + FUNC_LEAVE_NOAPI(borrow ? TRUE : FALSE); +} + + +/*------------------------------------------------------------------------- * Function: H5T_bit_neg * * Purpose: Bit-negate buffer. |