mirror of
https://github.com/notwa/mm
synced 2024-11-05 06:29:02 -08:00
44 lines
1.4 KiB
NASM
44 lines
1.4 KiB
NASM
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crc32:
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// this is a re-implementation of the C code
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// available at https://gist.github.com/notwa/5689243
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// a0: pointer to input data
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// a1: input data length
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// a2: existing crc value (use 0xFFFFFFFF for initialization)
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// v0: new crc value (bitwise NOT it when you're finished cycling)
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mov v0, a2
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la t9, crc32_constants
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-:
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lbu t0, (a0) // *ptr
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// first nybble
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//crc = (crc >> 4) ^ crc32_tbl[(crc & 0xf) ^ (*ptr & 0xf)];
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andi t2, v0, 0xF
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andi t3, t0, 0xF
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srl t1, v0, 4
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xor t4, t2, t3
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sll t5, t4, 2 // offset = index*sizeof(word)
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addu t6, t5, t9
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lw t7, (t6)
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xor v0, t1, t7
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// second nybble
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//crc = (crc >> 4) ^ crc32_tbl[(crc & 0xf) ^ (*(ptr++) >> 4)];
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andi t2, v0, 0xF
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srl t3, t0, 4
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srl t1, v0, 4
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xor t4, t2, t3
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sll t5, t4, 2 // offset = index*sizeof(word)
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addu t6, t5, t9
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lw t7, (t6)
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xor v0, t1, t7
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// iterate or return
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subi a1, a1, 1 // cnt--
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bnez a1, -
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addi a0, a0, 1 // ptr++
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jr
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nop
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crc32_constants: // ethernet standard (0x04C11DB7 as the crc divisor)
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.word 0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC
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.word 0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C
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.word 0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C
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.word 0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
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