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Commit0736fc1

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Clarify the choice of rscale in numeric_sqrt().
Improve the comment explaining the choice of rscale in numeric_sqrt(),and ensure that the code works consistently when other values ofNBASE/DEC_DIGITS are used.Note that, in practice, we always expect DEC_DIGITS == 4, and thisdoes not change the computation in that case.Joel Jacobson and Dean RasheedDiscussion:https://postgr.es/m/06712c29-98e9-43b3-98da-f234d81c6e49%40app.fastmail.com
1 parent9a84f29 commit0736fc1

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‎src/backend/utils/adt/numeric.c

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3693,8 +3693,21 @@ numeric_sqrt(PG_FUNCTION_ARGS)
36933693

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init_var(&result);
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3696-
/* Assume the input was normalized, so arg.weight is accurate */
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sweight= (arg.weight+1)*DEC_DIGITS /2-1;
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/*
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* Assume the input was normalized, so arg.weight is accurate. The result
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* then has at least sweight = floor(arg.weight * DEC_DIGITS / 2 + 1)
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* digits before the decimal point. When DEC_DIGITS is even, we can save
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* a few cycles, since the division is exact and there is no need to round
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* towards negative infinity.
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*/
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#ifDEC_DIGITS== ((DEC_DIGITS /2)*2)
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sweight=arg.weight*DEC_DIGITS /2+1;
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#else
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if (arg.weight >=0)
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sweight=arg.weight*DEC_DIGITS /2+1;
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else
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sweight=1- (1-arg.weight*DEC_DIGITS) /2;
3710+
#endif
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rscale=NUMERIC_MIN_SIG_DIGITS-sweight;
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rscale=Max(rscale,arg.dscale);

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