Lecture_7

# Lecture_7 - Chapter 2 Instructions Language of the Computer...

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Chapter 2 Instructions: Language of the Computer

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Chapter 2 — Instructions: Language of the Computer — 2 C Sort Example Illustrates use of assembly instructions for a C bubble sort function Swap procedure (leaf) void swap(int v[], int k) { int temp; temp = v[k]; v[k] = v[k+1]; v[k+1] = temp; } v in \$a0, k in \$a1, temp in \$t0 §2.13 A C Sort Example to Put It All Together
Chapter 2 — Instructions: Language of the Computer — 3 The Procedure Swap swap: sll \$t1, \$a1, 2 # \$t1 = k * 4 add \$t1, \$a0, \$t1 # \$t1 = v+(k*4) # (address of v[k]) lw \$t0, 0(\$t1) # \$t0 (temp) = v[k] lw \$t2, 4(\$t1) # \$t2 = v[k+1] sw \$t2, 0(\$t1) # v[k] = \$t2 (v[k+1]) sw \$t0, 4(\$t1) # v[k+1] = \$t0 (temp) jr \$ra # return to calling routine

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Chapter 2 — Instructions: Language of the Computer — 4 The Sort Procedure in C Non-leaf (calls swap) void sort (int v[], int n) { int i, j; for (i = 0; i < n; i += 1) { for (j = i – 1; j >= 0 && v[j] > v[j + 1]; j -= 1) { swap(v,j); } } } v in \$a0, n in \$a1, i in \$s0, j in \$s1
Chapter 2 — Instructions: Language of the Computer — 5 The Procedure Body move \$s2, \$a0 # save \$a0 into \$s2 move \$s3, \$a1 # save \$a1 into \$s3 move \$s0, \$zero # i = 0 for1tst: slt \$t0, \$s0, \$s3 # \$t0 = 0 if \$s0 \$s3 (i n) beq \$t0, \$zero, exit1 # go to exit1 if \$s0 \$s3 (i n) addi \$s1, \$s0, –1 # j = i – 1 for2tst: slti \$t0, \$s1, 0 # \$t0 = 1 if \$s1 < 0 (j < 0) bne \$t0, \$zero, exit2 # go to exit2 if \$s1 < 0 (j < 0) sll \$t1, \$s1, 2 # \$t1 = j * 4 add \$t2, \$s2, \$t1 # \$t2 = v + (j * 4) lw \$t3, 0(\$t2) # \$t3 = v[j] lw \$t4, 4(\$t2) # \$t4 = v[j + 1] slt \$t0, \$t4, \$t3 # \$t0 = 0 if \$t4 \$t3 beq \$t0, \$zero, exit2 # go to exit2 if \$t4 \$t3 move \$a0, \$s2 # 1st param of swap is v (old \$a0) move \$a1, \$s1 # 2nd param of swap is j jal swap # call swap procedure addi \$s1, \$s1, –1 # j –= 1 j for2tst # jump to test of inner loop exit2: addi \$s0, \$s0, 1 # i += 1 j for1tst # jump to test of outer loop Pass params & call Move params Inner loop Outer loop Inner loop Outer loop

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Chapter 2 — Instructions: Language of the Computer — 6 sort: addi \$sp,\$sp, –20 # make room on stack for 5 registers sw \$ra, 16(\$sp) # save \$ra on stack sw \$s3,12(\$sp) # save \$s3 on stack sw \$s2, 8(\$sp) # save \$s2 on stack sw \$s1, 4(\$sp) # save \$s1 on stack sw \$s0, 0(\$sp) # save \$s0 on stack # procedure body exit1: lw \$s0, 0(\$sp) # restore \$s0 from stack lw \$s1, 4(\$sp) # restore \$s1 from stack lw \$s2, 8(\$sp) # restore \$s2 from stack lw \$s3,12(\$sp) # restore \$s3 from stack lw \$ra,16(\$sp) # restore \$ra from stack addi \$sp,\$sp, 20 # restore stack pointer jr \$ra # return to calling routine The Full Procedure
Chapter 2 — Instructions: Language of the Computer — 7 Effect of Compiler Optimization

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