Add functions deposit32(), deposit64(), extract32() and extract64() to extract and deposit bitfields in 32 and 64 bit words. Based on ideas by Jia Liu and Avi Kivity.
Suggested-by: Jia Liu <pro...@gmail.com> Suggested-by: Avi Kivity <a...@redhat.com> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> --- Changes: v1->v2: added missing brackets v2->v3: renamed field32,field64 to extract32,extract64 added deposit32,deposit64 at Avi's suggestion fixed assertion as per Jay Foad's suggestion bikeshed roof is now a slightly darker shade of grey NB: the deposit functions differ slightly from Avi's proposal: * instead of taking a pointer which we modify, we return the updated value. (This matches the semantics of the TCG deposit op and also seems to me generally nicer) * the implementation permits deposits of the entire word (ie length 32/64) bitops.h | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 66 insertions(+), 0 deletions(-) diff --git a/bitops.h b/bitops.h index 07d1a06..5a44bb1 100644 --- a/bitops.h +++ b/bitops.h @@ -269,4 +269,70 @@ static inline unsigned long hweight_long(unsigned long w) return count; } +/** + * extract32 - 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 extract32(uint32_t value, int start, int length) +{ + assert(start >= 0 && length > 0 && length <= 32 - start); + return (value >> start) & (~0U >> (32 - length)); +} + +/** + * extract64 - 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 extract64(uint64_t value, int start, int length) +{ + assert(start >= 0 && length > 0 && length <= 64 - start); + return (value >> start) & (~0ULL >> (64 - length)); +} + +/** + * deposit32 - Insert into a specified bit field in a uint32_t + * @value: Initial value to insert bit field into + * @start: The lowest bit in the bit field (numbered from 0) + * @length: The length of the bit field + * @fieldval: The value to insert into the bit field + * + * Returns the input value with the fieldval inserted + * into it at the specified location. + */ +static inline uint32_t deposit32(uint32_t value, int start, int length, + uint32_t fieldval) +{ + uint32_t mask; + assert(start >= 0 && length > 0 && length <= 32 - start); + mask = (~0U >> (32 - length)) << start; + return (value & ~mask) | ((fieldval << start) & mask); +} + +/** + * deposit64 - Insert into a specified bit field in a uint64_t + * @value: Initial value to insert bit field into + * @start: The lowest bit in the bit field (numbered from 0) + * @length: The length of the bit field + * @fieldval: The value to insert into the bit field + * + * Returns the input value with the fieldval inserted + * into it at the specified location. + */ +static inline uint64_t deposit64(uint64_t value, int start, int length, + uint64_t fieldval) +{ + uint64_t mask; + assert(start >= 0 && length > 0 && length <= 64 - start); + mask = (~0ULL >> (64 - length)) << start; + return (value & ~mask) | ((fieldval << start) & mask); +} + #endif -- 1.7.1