Commit 2dc6bebd authored by Peter Maydell's avatar Peter Maydell Committed by Anthony Liguori
Browse files

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: default avatarPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: default avatarRichard Henderson <rth@twiddle.net>
Message-id: 1372419632-5521-2-git-send-email-peter.maydell@linaro.org
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent fd1d9926

include/qemu/bitops.h

+50 −0
Original line number Diff line number Diff line
@@ -221,6 +221,56 @@ static inline uint64_t extract64(uint64_t value, int start, int length) 
    return (value >> start) & (~0ULL >> (64 - 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