Re-using mpfr_t in long chain of arithmetic operations

Asked Feb 04 '14 at 02:28

Active Feb 04 '14 at 03:13

Viewed 42 times

I'm writing a function which uses mpfr_t as its main data type. In this function, there will be long chains of operations which need temporary variables to store intermediate results. I'd like to minimize the number of temporary variables I'll need, so I'm doing something like this:

mpfr_t tmp1;
mpfr_t tmp2;
mpfr_sub(tmp1, a, b, MPFR_RNDN);
mpfr_mul(tmp2, c, d, MPFR_RNDN);
mpfr_add(tmp2, tmp1, a, MPFR_RNDN);

Then later in the function:

mpfr_mul(tmp1, e, f, MPFR_RNDN);

Can I rely on the prior value of tmp1 being completely cleared from the variable when it is reassigned with e*f?

edited Feb 04 '14 at 03:13

asked Feb 04 '14 at 02:28

pg1989

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Yes, just like when you write z=x*y the previous value of z disappears. – Marc Glisse Feb 04 '14 at 11:01
I know that's the case for standard C/++ arithmetic, but is it also true for MPFR? – pg1989 Feb 04 '14 at 20:35
Yes (I already said that). What else would you expect? – Marc Glisse Feb 05 '14 at 12:19
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Nothing in particular, but in my experience the problems that really bite you in the ass are the ones you *don't* expect. – pg1989 Feb 05 '14 at 21:02

Re-using mpfr_t in long chain of arithmetic operations

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