diff options
Diffstat (limited to 'src/backend/utils/adt/numeric.c')
| -rw-r--r-- | src/backend/utils/adt/numeric.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c index bd00f23b946..10229eb37e9 100644 --- a/src/backend/utils/adt/numeric.c +++ b/src/backend/utils/adt/numeric.c @@ -8500,6 +8500,7 @@ ln_var(const NumericVar *arg, NumericVar *result, int rscale) NumericVar ni; NumericVar elem; NumericVar fact; + int nsqrt; int local_rscale; int cmp; @@ -8530,12 +8531,14 @@ ln_var(const NumericVar *arg, NumericVar *result, int rscale) * rscale as we work so that we keep this many significant digits at each * step (plus a few more for good measure). */ + nsqrt = 0; while (cmp_var(&x, &const_zero_point_nine) <= 0) { local_rscale = rscale - x.weight * DEC_DIGITS / 2 + 8; local_rscale = Max(local_rscale, NUMERIC_MIN_DISPLAY_SCALE); sqrt_var(&x, &x, local_rscale); mul_var(&fact, &const_two, &fact, 0); + nsqrt++; } while (cmp_var(&x, &const_one_point_one) >= 0) { @@ -8543,6 +8546,7 @@ ln_var(const NumericVar *arg, NumericVar *result, int rscale) local_rscale = Max(local_rscale, NUMERIC_MIN_DISPLAY_SCALE); sqrt_var(&x, &x, local_rscale); mul_var(&fact, &const_two, &fact, 0); + nsqrt++; } /* @@ -8555,8 +8559,12 @@ ln_var(const NumericVar *arg, NumericVar *result, int rscale) * * The convergence of this is not as fast as one would like, but is * tolerable given that z is small. + * + * The Taylor series result will be multiplied by 2^(nsqrt+1), which has a + * decimal weight of (nsqrt+1) * log10(2), so work with this many extra + * digits of precision (plus a few more for good measure). */ - local_rscale = rscale + 8; + local_rscale = rscale + (int) ((nsqrt + 1) * 0.301029995663981) + 8; sub_var(&x, &const_one, result); add_var(&x, &const_one, &elem); |