From 2dc6bebde93677b262caff114849d0f5ebdaa82d Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Fri, 28 Jun 2013 12:40:31 +0100 Subject: [PATCH] bitops: Provide sextract32() and sextract64() A common operation in instruction decoding is to take a field from an instruction that represents a signed integer in some arbitrary number of bits, and sign extend it into a C signed integer type for manipulation. Provide new functions sextract32() and sextract64() which perform this operation; they are like the existing extract32() and extract64() except that the field is sign-extended into the returned result. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Message-id: 1372419632-5521-2-git-send-email-peter.maydell@linaro.org Signed-off-by: Anthony Liguori --- include/qemu/bitops.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h index affcc969dc..06e2e6f0ee 100644 --- a/include/qemu/bitops.h +++ b/include/qemu/bitops.h @@ -222,6 +222,56 @@ static inline uint64_t extract64(uint64_t value, int start, int length) } /** + * sextract32: + * @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 + * + * Extract from the 32 bit input @value the bit field specified by the + * @start and @length parameters, and return it, sign extended to + * an int32_t (ie with the most significant bit of the field propagated + * to all the upper bits of the return value). The bit field must lie + * entirely within the 32 bit word. It is valid to request that + * all 32 bits are returned (ie @length 32 and @start 0). + * + * Returns: the sign extended value of the bit field extracted from the + * input value. + */ +static inline int32_t sextract32(uint32_t value, int start, int length) +{ + assert(start >= 0 && length > 0 && length <= 32 - start); + /* Note that this implementation relies on right shift of signed + * integers being an arithmetic shift. + */ + return ((int32_t)(value << (32 - length - start))) >> (32 - length); +} + +/** + * sextract64: + * @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 + * + * Extract from the 64 bit input @value the bit field specified by the + * @start and @length parameters, and return it, sign extended to + * an int64_t (ie with the most significant bit of the field propagated + * to all the upper bits of the return value). The bit field must lie + * entirely within the 64 bit word. It is valid to request that + * all 64 bits are returned (ie @length 64 and @start 0). + * + * Returns: the sign extended value of the bit field extracted from the + * input value. + */ +static inline uint64_t sextract64(uint64_t value, int start, int length) +{ + assert(start >= 0 && length > 0 && length <= 64 - start); + /* Note that this implementation relies on right shift of signed + * integers being an arithmetic shift. + */ + return ((int64_t)(value << (64 - length - start))) >> (64 - length); +} + +/** * deposit32: * @value: initial value to insert bit field into * @start: the lowest bit in the bit field (numbered from 0) -- 2.11.4.GIT