Bit Operations
This section describes functions and operators for examining and manipulating bits of a given variable (or value).
Related GPC Functions:
1. set_bit
Set one bit of a variable, based on bit position.
Prototype:
set_bit ( <variable>, <bit_index> )
Parameters:
<variable> : any defined variable
<bit_index> : position of the bit to be set in <variable>, range [0~15]
Return:
None
Example:
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set_bit(x, 3);
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2. clear_bit
Clear one bit of a variable, based on bit position.
Prototype:
clear_bit ( <variable>, <bit_index> )
Parameters:
<variable> : any defined variable
<bit_index> : position of the bit to be clear in <variable>, range [0~15]
Return:
None
Example:
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clear_bit(x, 9);
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3. test_bit
Test a bit into of a variable (or value), based on bit position.
Prototype:
int test_bit ( <value>, <bit_index> )
Parameters:
<value> : anything that has a value (constants, variables, functions, expressions, etc...)
<bit_index> : position of the bit to be tested in <value>, range [0~15]
Return:
True if the bit is set, false otherwise
Example:
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if(test_bit(x, 12)) {
// Do something
}
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4. set_bits
Store a value into a variable, based on bit position and a bit mask.
Prototype:
set_bits ( <variable>, <value>, <bit_index>, <bit_mask> )
Parameters:
<variable> : any defined variable
<value> : anything that has a value (constants, variables, functions, expressions, etc...)
<bit_index> : position of the less significant bit in the value to store, range [0~15]
<bit_mask> : bit mask corresponding to the size, in bits, of the value to store (without shifting)
Return:
None
Example:
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int m = 0, n = 0;
main {
set_bits(m, 5, 4, 15); // bit_mask = 15, 0x000F,
// m = 80 (0x0050) 0b0000'0000'0000'1111
set_bits(m, 109, 8, 255); // bit_mask = 255, 0x00FF,
// m = 27984 (0x6D50) 0b0000'0000'1111'1111
n = get_bits(m, 4, 15); // n = 5
}
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5. get_bits
Extract a value from a variable (or a given value defined by a expression), based on bit position and a bit mask.
Prototype:
int get_bits ( <expression>, <bit_index>, <bit_mask> )
Parameters:
<expression> : a variable or anything that has a value
<bit_index> : position of the less significant bit in the value to extract, range [0~15]
<bit_mask> : bit mask corresponding to the size, in bits, of the value to extract (without shifting)
Return:
returns the value of a subset of bits in <expression>, the subset is defined by <bit_index> and <bit_mask>
Example:
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int m = 0, n = 0;
main {
set_bits(m, 5, 4, 15); // bit_mask = 15, 0x000F,
// m = 80 (0x0050) 0b0000'0000'0000'1111
set_bits(m, 109, 8, 255); // bit_mask = 255, 0x00FF,
// m = 27984 (0x6D50) 0b0000'0000'1111'1111
n = get_bits(m, 8, 255); // n = 109
}
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