324_Book

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Unformatted text preview: (*hi), "=r" (*lo) /* and move results to */ : /* No input */ /* the two outputs */ : "%edx", "%eax"); } /* Record the current value of the cycle counter. */ void start_counter() { access_counter(&cyc_hi, &cyc_lo); } /* Return the number of cycles since the last call to start_counter. */ double get_counter() { unsigned ncyc_hi, ncyc_lo; unsigned hi, lo, borrow; double result; /* Get cycle counter */ access_counter(&ncyc_hi, &ncyc_lo); /* Do double precision subtraction */ lo = ncyc_lo - cyc_lo; borrow = lo > ncyc_lo; hi = ncyc_hi - cyc_hi - borrow; result = (double) hi * (1 << 30) * 4 + lo; if (result < 0) { fprintf(stderr, "Error: counter returns neg value: %.0f\n", result); } return result; } code/perf/clock.c Figure 9.9: Code Implementing Program Interface to IA32 Cycle Counter Assembly code is required to make use of the counter reading instruction. 462 CHAPTER 9. MEASURING PROGRAM EXECUTION TIME code/perf/clock.c 1 2 3 4 5 6 7 8 9 10 11 12 13 /* Estimate the clock rate by measuri...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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