On 06/27/2012 01:29 PM, Peter Maydell wrote: > Add field32() and field64() functions which extract a particular > bit field from a word and return it. Based on an idea by Jia Liu. > > > +/** > + * field64 - return a specified bit field from a uint64_t value > + * @value: The value to extract the bit field from > + * @start: The lowest bit in the bit field (numbered from 0) > + * @length: The length of the bit field > + * > + * Returns the value of the bit field extracted from the input value. > + */ > +static inline uint64_t field64(uint64_t value, int start, int length) > +{ > + assert(start >= 0 && start <= 63 && length > 0 && start + length <= 64); > + return (value >> start) & (~0ULL >> (64 - length)); > +} > +
Undefined for length == 64, so better add that to the assert. I suggest adding the analogous functions for writing. I believe the common naming is extract/deposit. static inline uint64_t deposit64(uint64_t *pvalue, unsigned start, unsigned length, uint64_t fieldval) { uint64_t mask = (((uint64_t)1 << length) - 1) << start; *pvalue = (*pvalue & ~mask) | ((fieldval << start) & mask); } Useful for setting a bit to a specific value. -- error compiling committee.c: too many arguments to function