Bit_Operations

macOSLinuxWindowswasm

#import "Bit_Operations";

Byte swapping, bit scans and population count for integers of any size.

Procedures#

(input: $T) -> T

Reverses the byte order of input and returns the result; input is untouched.

assert(byte_swap(cast(u32) 0x11223344) == 0x44332211);
assert(byte_swap(cast(u16) 0x00ff) == 0xff00);
assert(byte_swap(byte_swap(cast(u64) 0x0102030405060708)) == 0x0102030405060708);

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byte_swap_in_place

(input: *$T)

Reverses the byte order of input where it is stored, the in-place form of byte_swap.

value: u32 = 0xAABBCCDD;
byte_swap_in_place(*value);
assert(value == 0xDDCCBBAA);

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bit_scan_forward

(input: $T) -> s32

The 1-based position of the lowest set bit of input: 1 for bit 0, 4 for bit 3. Returns 0 when no bit is set.

assert(bit_scan_forward(cast(u32) 1) == 1);
assert(bit_scan_forward(cast(u32) 0b1000) == 4);
assert(bit_scan_forward(cast(u8) 0b1010_0000) == 6);
assert(bit_scan_forward(cast(u32) 0) == 0);

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bit_scan_reverse

(input: $T) -> s32

The 1-based position of the highest set bit of input, which is also the number of bits needed to hold it (so floor(log2) plus one). Returns 0 when no bit is set.

assert(bit_scan_reverse(cast(u32) 1) == 1);
assert(bit_scan_reverse(cast(u32) 0b1000) == 4);
assert(bit_scan_reverse(cast(u64) 0xFFFF_FFFF_FFFF_FFFF) == 64);
assert(bit_scan_reverse(cast(s16) -1) == 16);
assert(bit_scan_reverse(cast(u32) 0) == 0);

↗

popcount

(value: $T) -> s32

The number of bits set in value, counting only its size_of(T) bytes.

assert(popcount(cast(u32) 0) == 0);
assert(popcount(cast(u32) 0b1011) == 3);
assert(popcount(cast(s8) -1) == 8);
assert(popcount(cast(u64) 0xFFFF_FFFF_FFFF_FFFF) == 64);

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