Add field32() and field64() functions which extract a particular bit field from a word and return it. Based on an idea by Jia Liu.
Suggested-by: Jia Liu <pro...@gmail.com> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> --- v1->v2: added missing brackets to field32() to bring it in to line with field64() (Still using 'int' rather than 'unsigned' for bit numbers as per rationale in previous discussion.) bitops.h | 28 ++++++++++++++++++++++++++++ 1 files changed, 28 insertions(+), 0 deletions(-) diff --git a/bitops.h b/bitops.h index 07d1a06..ffbb387 100644 --- a/bitops.h +++ b/bitops.h @@ -269,4 +269,32 @@ static inline unsigned long hweight_long(unsigned long w) return count; } +/** + * 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)); +} + +/** + * field32 - return a specified bit field from a uint32_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 uint32_t field32(uint32_t value, int start, int length) +{ + assert(start >= 0 && start <= 31 && length > 0 && start + length <= 32); + return (value >> start) & (~0U >> (32 - length)); +} + #endif -- 1.7.1