73 lines
1.4 KiB
NASM
73 lines
1.4 KiB
NASM
pub rotate_left:
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; (r1 >> r2) | (r1 << (32 - r2))
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sub r3, zr, r2
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add r3, r3, 32
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lsr r3, r1, r3
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lsl r1, r1, r2
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or r1, r1, r3
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jmp r13
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pub rotate_right:
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; (r1 << r2) | (r1 >> (32 - r2))
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sub r3, zr, r2
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add r3, r3, 32
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lsl r3, r1, r3
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lsr r1, r1, r2
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or r1, r1, r3
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jmp r13
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pub clz:
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; special case
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mov r4, 0
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; since we start the loop by shifting r2 load twice the value we need
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mov r2, 32
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mov r3, r1
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; divide and conquer algorithm
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clz_loop:
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; next finer step
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lsr r2, r2, 1
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; abort if there is no finer step
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cmp r2, 0
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je clz_end
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; see if there are still some 1 bits left with this additional shift
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lsr r3, r3, r2
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add r4, r4, r2
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cmp r3, 0
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jne clz_loop
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; undo shift if it resulted in zero
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sub r4, r4, r2
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lsr r3, r1, r4
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jmp clz_loop
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clz_end:
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; we calculated the position of the last 1 from the least significant side
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; inverse is what we want (position of last 0 from most significant side)
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mov r1, 31
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sub r1, r1, r4
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jmp r13
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pub popc:
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mov r2, 0x0101 ; load mask of 0x01010101
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lsl r2, r2, 16
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or r2, r2, 0x0101
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mov r3, 8 ; bits in byte
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mov r4, 0 ; pop count of each byte
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popc_loop:
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and r5, r1, r2 ; extract least significant bit of byte
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add r4, r4, r5
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lsr r1, r1, 1 ; cycle through bits
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sub r3, r3, 1
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cmp r3, 0
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jg popc_loop
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; sum up bytes
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lsr r2, r4, 8
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add r4, r4, r2
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lsr r2, r4, 16
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add r4, r4, r2
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and r1, r4, 0xFF ; mask out end result in lowest byte
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jmp r13
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