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bitops.h: Add functions to extract and deposit bitfields

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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 <proljc@gmail.com>
Suggested-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
This commit is contained in:
Peter Maydell 2012-07-06 15:48:00 +01:00 committed by Blue Swirl
parent bedc2ac1a7
commit 84988cf910
1 changed files with 90 additions and 0 deletions
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bitops.h
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@ -269,4 +269,94 @@ static inline unsigned long hweight_long(unsigned long w)
return count;
}
/**
* extract32:
* @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. 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 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:
* @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. 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 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:
* @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
*
* Deposit @fieldval into the 32 bit @value at the bit field specified
* by the @start and @length parameters, and return the modified
* @value. Bits of @value outside the bit field are not modified.
* Bits of @fieldval above the least significant @length bits are
* ignored. The bit field must lie entirely within the 32 bit word.
* It is valid to request that all 64 bits are modified (ie @length
* 64 and @start 0).
*
* Returns: the modified @value.
*/
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);
}
/**
* deposit32:
* @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
*
* Deposit @fieldval into the 64 bit @value at the bit field specified
* by the @start and @length parameters, and return the modified
* @value. Bits of @value outside the bit field are not modified.
* Bits of @fieldval above the least significant @length bits are
* ignored. The bit field must lie entirely within the 32 bit word.
* It is valid to request that all 64 bits are modified (ie @length
* 64 and @start 0).
*
* Returns: the modified @value.
*/
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