CHAPTER FIVE
SORTING
EXERCISES
[6]
6. [15] Mr. B. C. Dull (an MMIX programmer) wanted to know if the number stored in location A is greater than, less than, or equal to the number stored in location B. So he wrote ‘LDO $0,A; LDO $1,B; SUB $2,$0,$1’ and tested whether register $2 was positive, negative, or zero. What serious mistake did he make, and what should he have done instead?
7. [17] Write an MMIX subroutine MCmp for multiprecision comparison of n-byte keys (an−1, . . . , a0) and (bn−1, . . . , b0), where ai and bi are unsigned bytes stored in order of increasing index i. Use the following specification:
| Calling sequence: | PUSHJ t,MCmp |
| Entry conditions: | $0 ≡ n; $1 ≡ LOC(a0); and $2 ≡ LOC(b0) |
| Return value: | 1, if (an–1, . . . , a0) < ... |
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