Bitwise operations¶
The header qemu/bitops.h
provides utility functions for
performing bitwise operations.

void
set_bit
(long nr, unsigned long *addr)¶ Set a bit in memory
Parameters
long nr
the bit to set
unsigned long *addr
the address to start counting from

void
set_bit_atomic
(long nr, unsigned long *addr)¶ Set a bit in memory atomically
Parameters
long nr
the bit to set
unsigned long *addr
the address to start counting from

void
clear_bit
(long nr, unsigned long *addr)¶ Clears a bit in memory
Parameters
long nr
Bit to clear
unsigned long *addr
Address to start counting from

void
change_bit
(long nr, unsigned long *addr)¶ Toggle a bit in memory
Parameters
long nr
Bit to change
unsigned long *addr
Address to start counting from

int
test_and_set_bit
(long nr, unsigned long *addr)¶ Set a bit and return its old value
Parameters
long nr
Bit to set
unsigned long *addr
Address to count from

int
test_and_clear_bit
(long nr, unsigned long *addr)¶ Clear a bit and return its old value
Parameters
long nr
Bit to clear
unsigned long *addr
Address to count from

int
test_and_change_bit
(long nr, unsigned long *addr)¶ Change a bit and return its old value
Parameters
long nr
Bit to change
unsigned long *addr
Address to count from

int
test_bit
(long nr, const unsigned long *addr)¶ Determine whether a bit is set
Parameters
long nr
bit number to test
const unsigned long *addr
Address to start counting from

unsigned long
find_last_bit
(const unsigned long *addr, unsigned long size)¶ find the last set bit in a memory region
Parameters
const unsigned long *addr
The address to start the search at
unsigned long size
The maximum size to search
Description
Returns the bit number of the first set bit, or size.

unsigned long
find_next_bit
(const unsigned long *addr, unsigned long size, unsigned long offset)¶ find the next set bit in a memory region
Parameters
const unsigned long *addr
The address to base the search on
unsigned long size
The bitmap size in bits
unsigned long offset
The bitnumber to start searching at

unsigned long
find_next_zero_bit
(const unsigned long *addr, unsigned long size, unsigned long offset)¶ find the next cleared bit in a memory region
Parameters
const unsigned long *addr
The address to base the search on
unsigned long size
The bitmap size in bits
unsigned long offset
The bitnumber to start searching at

unsigned long
find_first_bit
(const unsigned long *addr, unsigned long size)¶ find the first set bit in a memory region
Parameters
const unsigned long *addr
The address to start the search at
unsigned long size
The maximum size to search
Description
Returns the bit number of the first set bit.

unsigned long
find_first_zero_bit
(const unsigned long *addr, unsigned long size)¶ find the first cleared bit in a memory region
Parameters
const unsigned long *addr
The address to start the search at
unsigned long size
The maximum size to search
Description
Returns the bit number of the first cleared bit.

uint8_t
rol8
(uint8_t word, unsigned int shift)¶ rotate an 8bit value left
Parameters
uint8_t word
value to rotate
unsigned int shift
bits to roll

uint8_t
ror8
(uint8_t word, unsigned int shift)¶ rotate an 8bit value right
Parameters
uint8_t word
value to rotate
unsigned int shift
bits to roll

uint16_t
rol16
(uint16_t word, unsigned int shift)¶ rotate a 16bit value left
Parameters
uint16_t word
value to rotate
unsigned int shift
bits to roll

uint16_t
ror16
(uint16_t word, unsigned int shift)¶ rotate a 16bit value right
Parameters
uint16_t word
value to rotate
unsigned int shift
bits to roll

uint32_t
rol32
(uint32_t word, unsigned int shift)¶ rotate a 32bit value left
Parameters
uint32_t word
value to rotate
unsigned int shift
bits to roll

uint32_t
ror32
(uint32_t word, unsigned int shift)¶ rotate a 32bit value right
Parameters
uint32_t word
value to rotate
unsigned int shift
bits to roll

uint64_t
rol64
(uint64_t word, unsigned int shift)¶ rotate a 64bit value left
Parameters
uint64_t word
value to rotate
unsigned int shift
bits to roll

uint64_t
ror64
(uint64_t word, unsigned int shift)¶ rotate a 64bit value right
Parameters
uint64_t word
value to rotate
unsigned int shift
bits to roll

uint32_t
extract32
(uint32_t value, int start, int length)¶
Parameters
uint32_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
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).
Return
the value of the bit field extracted from the input value.

uint8_t
extract8
(uint8_t value, int start, int length)¶
Parameters
uint8_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
Extract from the 8 bit input value the bit field specified by the start and length parameters, and return it. The bit field must lie entirely within the 8 bit word. It is valid to request that all 8 bits are returned (ie length 8 and start 0).
Return
the value of the bit field extracted from the input value.

uint16_t
extract16
(uint16_t value, int start, int length)¶
Parameters
uint16_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
Extract from the 16 bit input value the bit field specified by the start and length parameters, and return it. The bit field must lie entirely within the 16 bit word. It is valid to request that all 16 bits are returned (ie length 16 and start 0).
Return
the value of the bit field extracted from the input value.

uint64_t
extract64
(uint64_t value, int start, int length)¶
Parameters
uint64_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
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).
Return
the value of the bit field extracted from the input value.

int32_t
sextract32
(uint32_t value, int start, int length)¶
Parameters
uint32_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
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).
Return
the sign extended value of the bit field extracted from the input value.

int64_t
sextract64
(uint64_t value, int start, int length)¶
Parameters
uint64_t value
the value to extract the bit field from
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
Description
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).
Return
the sign extended value of the bit field extracted from the input value.

uint32_t
deposit32
(uint32_t value, int start, int length, uint32_t fieldval)¶
Parameters
uint32_t value
initial value to insert bit field into
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
uint32_t fieldval
the value to insert into the bit field
Description
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 32 bits are modified (ie length 32 and start 0).
Return
the modified value.

uint64_t
deposit64
(uint64_t value, int start, int length, uint64_t fieldval)¶
Parameters
uint64_t value
initial value to insert bit field into
int start
the lowest bit in the bit field (numbered from 0)
int length
the length of the bit field
uint64_t fieldval
the value to insert into the bit field
Description
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 64 bit word. It is valid to request that all 64 bits are modified (ie length 64 and start 0).
Return
the modified value.

uint32_t
half_shuffle32
(uint32_t x)¶
Parameters
uint32_t x
32bit value (of which only the bottom 16 bits are of interest)
Description
Given an input value:
xxxx xxxx xxxx xxxx ABCD EFGH IJKL MNOP
return the value where the bottom 16 bits are spread out into the odd bits in the word, and the even bits are zeroed:
0A0B 0C0D 0E0F 0G0H 0I0J 0K0L 0M0N 0O0P
Any bits set in the top half of the input are ignored.
Return
the shuffled bits.

uint64_t
half_shuffle64
(uint64_t x)¶
Parameters
uint64_t x
64bit value (of which only the bottom 32 bits are of interest)
Description
Given an input value:
xxxx xxxx xxxx .... xxxx xxxx ABCD EFGH IJKL MNOP QRST UVWX YZab cdef
return the value where the bottom 32 bits are spread out into the odd bits in the word, and the even bits are zeroed:
0A0B 0C0D 0E0F 0G0H 0I0J 0K0L 0M0N .... 0U0V 0W0X 0Y0Z 0a0b 0c0d 0e0f
Any bits set in the top half of the input are ignored.
Return
the shuffled bits.

uint32_t
half_unshuffle32
(uint32_t x)¶
Parameters
uint32_t x
32bit value (of which only the odd bits are of interest)
Description
Given an input value:
xAxB xCxD xExF xGxH xIxJ xKxL xMxN xOxP
return the value where all the odd bits are compressed down into the low half of the word, and the high half is zeroed:
0000 0000 0000 0000 ABCD EFGH IJKL MNOP
Any even bits set in the input are ignored.
Return
the unshuffled bits.

uint64_t
half_unshuffle64
(uint64_t x)¶
Parameters
uint64_t x
64bit value (of which only the odd bits are of interest)
Description
Given an input value:
xAxB xCxD xExF xGxH xIxJ xKxL xMxN .... xUxV xWxX xYxZ xaxb xcxd xexf
return the value where all the odd bits are compressed down into the low half of the word, and the high half is zeroed:
0000 0000 0000 .... 0000 0000 ABCD EFGH IJKL MNOP QRST UVWX YZab cdef
Any even bits set in the input are ignored.
Return
the unshuffled bits.