135 lines
3.3 KiB
C
135 lines
3.3 KiB
C
#include <stdio.h>
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typedef unsigned int u32;
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u32 arm_imm_find_nonzero(u32 imm, u32 start_bit)
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{
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u32 i;
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for(i = start_bit; i < 32; i += 2)
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{
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if((imm >> i) & 0x03)
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break;
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}
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return i;
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}
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u32 arm_disect_imm_32bit(u32 imm, u32 *stores, u32 *rotations)
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{
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u32 store_count = 0;
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u32 left_shift = 0;
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// Otherwise it'll return 0 things to store because it'll never
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// find anything.
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if(imm == 0)
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{
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rotations[0] = 0;
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stores[0] = 0;
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return 1;
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}
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// Find chunks of non-zero data at 2 bit alignments.
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while(1)
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{
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left_shift = arm_imm_find_nonzero(imm, left_shift);
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if(left_shift == 32)
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{
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// We've hit the end of the useful data.
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return store_count;
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}
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// Hit the end, it might wrap back around to the beginning.
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if(left_shift >= 24)
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{
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// Make a mask for the residual bits. IE, if we have
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// 5 bits of data at the end we can wrap around to 3
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// bits of data in the beginning. Thus the first
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// thing, after being shifted left, has to be less
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// than 111b, 0x7, or (1 << 3) - 1.
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u32 top_bits = 32 - left_shift;
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u32 residual_bits = 8 - top_bits;
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u32 residual_mask = (1 << residual_bits) - 1;
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if((store_count > 1) && (left_shift > 24) &&
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((stores[0] << (32 - rotations[0])) < residual_mask))
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{
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// Then we can throw out the last bit and tack it on
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// to the first bit.
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u32 initial_bits = rotations[0];
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stores[0] = (stores[0] << (top_bits + (32 - rotations[0]))) |
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((imm >> left_shift) & 0xFF);
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rotations[0] = top_bits;
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return store_count;
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}
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else
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{
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// There's nothing to wrap over to in the beginning
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stores[store_count] = (imm >> left_shift) & 0xFF;
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rotations[store_count] = (32 - left_shift) & 0x1F;
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return store_count + 1;
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}
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break;
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}
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stores[store_count] = (imm >> left_shift) & 0xFF;
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rotations[store_count] = (32 - left_shift) & 0x1F;
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store_count++;
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left_shift += 8;
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}
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}
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#define ror(value, shift) \
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((value) >> shift) | ((value) << (32 - shift)) \
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u32 arm_assemble_imm_32bit(u32 *stores, u32 *rotations, u32 store_count)
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{
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u32 n = ror(stores[0], rotations[0]);
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u32 i;
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printf("%x : %x\n", stores[0], rotations[0]);
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for(i = 1; i < store_count; i++)
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{
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printf("%x : %x\n", stores[i], rotations[i]);
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n |= ror(stores[i], rotations[i]);
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}
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return n;
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}
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int main(int argc, char *argv[])
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{
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u32 n = 0;
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u32 stores[4];
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u32 rotations[4];
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u32 store_count;
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u32 n2;
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if(argc != 1)
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{
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n = strtoul(argv[1], NULL, 16);
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store_count = arm_disect_imm_32bit(n, stores, rotations);
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n2 = arm_assemble_imm_32bit(stores, rotations, store_count);
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printf("%08x -> %08x (%d stores)\n", n, n2, store_count);
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return 0;
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}
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do
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{
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store_count = arm_disect_imm_32bit(n, stores, rotations);
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n2 = arm_assemble_imm_32bit(stores, rotations, store_count);
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if(n != n2)
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{
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printf("Failure: %08x -/-> %08x\n", n, n2);
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return -1;
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}
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n++;
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} while(n != 0);
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printf("Done!\n");
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return 0;
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}
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