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bpo-41513: Improve order of adding fractional values. Improve variable names. #22368

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Sep 23, 2020
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bpo-41513: Improve order of adding fractional values. Improve variable names. #22368

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24 changes: 12 additions & 12 deletions Modules/mathmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2502,8 +2502,8 @@ exactly equal) was verified for 1 billion random inputs with n=5. [7]
static inline double
vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
{
const double T27 = 134217729.0; /* ldexp(1.0, 27)+1.0) */
double x, csum = 1.0, oldcsum, scale, frac=0.0, frac_mid=0.0, frac_lo=0.0;
const double T27 = 134217729.0; /* ldexp(1.0, 27) + 1.0) */
double x, scale, oldcsum, csum = 1.0, frac1 = 0.0, frac2 = 0.0, frac3 = 0.0;
double t, hi, lo, h;
int max_e;
Py_ssize_t i;
Expand Down Expand Up @@ -2539,18 +2539,18 @@ vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac += (oldcsum - csum) + x;
frac1 += (oldcsum - csum) + x;

x = 2.0 * hi * lo;
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac_mid += (oldcsum - csum) + x;
frac2 += (oldcsum - csum) + x;

assert(csum + lo * lo == csum);
frac_lo += lo * lo;
frac3 += lo * lo;
}
h = sqrt(csum - 1.0 + (frac_lo + frac_mid + frac));
h = sqrt(csum - 1.0 + (frac1 + frac2 + frac3));

x = h;
t = x * T27;
Expand All @@ -2562,21 +2562,21 @@ vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac += (oldcsum - csum) + x;
frac1 += (oldcsum - csum) + x;

x = -2.0 * hi * lo;
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac_mid += (oldcsum - csum) + x;
frac2 += (oldcsum - csum) + x;

x = -lo * lo;
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac_lo += (oldcsum - csum) + x;
frac3 += (oldcsum - csum) + x;

x = csum - 1.0 + (frac_lo + frac_mid + frac);
x = csum - 1.0 + (frac1 + frac2 + frac3);
return (h + x / (2.0 * h)) / scale;
}
/* When max_e < -1023, ldexp(1.0, -max_e) overflows.
Expand All @@ -2591,9 +2591,9 @@ vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
assert(fabs(csum) >= fabs(x));
oldcsum = csum;
csum += x;
frac += (oldcsum - csum) + x;
frac1 += (oldcsum - csum) + x;
}
return max * sqrt(csum - 1.0 + frac);
return max * sqrt(csum - 1.0 + frac1);
}

#define NUM_STACK_ELEMS 16
Expand Down