71 lines
2.0 KiB
ArmAsm
71 lines
2.0 KiB
ArmAsm
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/*
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* copy "upwards", increasing destination and source addresses
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*/
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fel_memcpy_up:
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ldr r0, 1f /* dst_addr */
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ldr r1, 2f /* src_addr */
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ldr r2, 3f /* bytes */
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sub r3, r1, r0
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tst r3, #3 /* test LSB for word alignment */
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bne copyup_tail /* unaligned access, copy byte-wise */
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copyup_head:
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tst r1, #3 /* word boundary? */
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beq copyup_loop
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ldrb r3, [r1], #1 /* load and post-inc */
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strb r3, [r0], #1 /* store and post-inc */
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subs r2, #1 /* r2 -= 1 */
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bpl copyup_head
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bx lr /* early return on small byte count (r2 < 0) */
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copyup_loop:
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subs r2, #4 /* r2 -= 4 */
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ldrpl r3, [r1], #4 /* load and post-inc */
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strpl r3, [r0], #4 /* store and post-inc */
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bpl copyup_loop /* while (r2 >= 0) */
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add r2, #4 /* r2 = remaining byte count */
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copyup_tail:
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subs r2, #1 /* r2 -= 1 */
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bxmi lr /* return on (r2 < 0) */
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ldrb r3, [r1], #1 /* load and post-inc */
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strb r3, [r0], #1 /* store and post-inc */
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b copyup_tail
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1: .word 0 /* dst_addr */
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2: .word 0 /* src_addr */
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3: .word 0 /* bytes */
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/*
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* copy "downwards", using base-relative indexing
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*/
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fel_memcpy_down:
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ldr r0, 1f /* dst_addr */
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ldr r1, 2f /* src_addr */
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ldr r2, 3f /* bytes */
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sub r3, r0, r1
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tst r3, #3 /* test LSB for word alignment */
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bne copydn_tail /* unaligned access, copy byte-wise */
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copydn_head:
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add r3, r1, r2 /* r3 = r1 + r2, for alignment check */
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tst r3, #3 /* word boundary? */
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beq copydn_loop
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subs r2, #1 /* r2 -= 1 */
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bxmi lr /* early return on small byte count (r2 < 0) */
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ldrb r3, [r1, r2] /* load byte */
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strb r3, [r0, r2] /* store byte */
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b copydn_head
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copydn_loop:
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subs r2, #4 /* r2 -= 4 */
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ldrpl r3, [r1, r2] /* load word */
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strpl r3, [r0, r2] /* store word */
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bpl copydn_loop /* while (r2 >= 0) */
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add r2, #4 /* r2 = remaining byte count */
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copydn_tail:
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subs r2, #1 /* r2 -= 1 */
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bxmi lr /* return on (r2 < 0) */
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ldrb r3, [r1, r2] /* load byte */
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strb r3, [r0, r2] /* store byte */
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b copydn_tail
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1: .word 0 /* dst_addr */
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2: .word 0 /* src_addr */
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3: .word 0 /* bytes */
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