From f578051209ec952873795beabadd40b54dbf182a Mon Sep 17 00:00:00 2001 From: Dean Rasheed Date: Sun, 20 Feb 2022 18:10:25 +0000 Subject: [PATCH 3/3] Use div_var() instead of div_var_fast() when the divisor is small. When the divisor contains just one base-NBASE digit, div_var() is much faster than div_var_fast(), since it contains special fast-path code for that case, and when the divisor has two digits, div_var() is still somewhat faster, since div_var_fast() has more overhead intended for larger inputs. Therefore, use div_var() instead of div_var_fast() in such cases. Where we know for sure that the divisor is small, such as the denominators of Taylor series terms, just call div_var() directly. Otherwise, have div_var_fast() delegate to div_var() when the divisor is small. This produces a noticeable speedup of exp(), ln() and the numeric-big regression test. --- src/backend/utils/adt/numeric.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c index 909f4eed74..3c1e310ce2 100644 --- a/src/backend/utils/adt/numeric.c +++ b/src/backend/utils/adt/numeric.c @@ -8725,6 +8725,16 @@ div_var_fast(const NumericVar *var1, const NumericVar *var2, NumericDigit *var1digits = var1->digits; NumericDigit *var2digits = var2->digits; + /* + * If the divisor has just one or two base-NBASE digits, it is + * significantly faster to just use div_var(). + */ + if (var2ndigits <= 2) + { + div_var(var1, var2, result, rscale, round); + return; + } + /* * First of all division by zero check; we must not be handed an * unnormalized divisor. @@ -9840,7 +9850,7 @@ exp_var(const NumericVar *arg, NumericVar *result, int rscale) } local_rscale = x.dscale + ndiv2; - div_var_fast(&x, &tmp, &x, local_rscale, true); + div_var(&x, &tmp, &x, local_rscale, true); free_var(&tmp); } @@ -9871,7 +9881,7 @@ exp_var(const NumericVar *arg, NumericVar *result, int rscale) mul_var(&x, &x, &elem, local_rscale); set_var_from_var(&const_two, &ni); - div_var_fast(&elem, &ni, &elem, local_rscale, true); + div_var(&elem, &ni, &elem, local_rscale, true); while (elem.ndigits != 0) { @@ -9879,7 +9889,7 @@ exp_var(const NumericVar *arg, NumericVar *result, int rscale) mul_var(&elem, &x, &elem, local_rscale); add_var(&ni, &const_one, &ni); - div_var_fast(&elem, &ni, &elem, local_rscale, true); + div_var(&elem, &ni, &elem, local_rscale, true); } /* @@ -10079,7 +10089,7 @@ ln_var(const NumericVar *arg, NumericVar *result, int rscale) { add_var(&ni, &const_two, &ni); mul_var(&xx, &x, &xx, local_rscale); - div_var_fast(&xx, &ni, &elem, local_rscale, true); + div_var(&xx, &ni, &elem, local_rscale, true); if (elem.ndigits == 0) break; -- 2.26.2