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Cleanup: replace macro by inline function in gas-model.c

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Replace a macro calculating a degree-three polynomial by an
inline function.

Moreover, calculate the powers 1, 2 and 3 of the pressure inside
the function. The compiler will be smart enough to optimize this
to the same code. The only important thing is to write "x*x*x*coeff"
instead of "coeff*x*x*x". The compiler can't optimize the latter
because ... wonderful floating point semantics.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
This commit is contained in:
Berthold Stoeger 2019-08-07 22:28:31 +02:00 • committed by Dirk Hohndel
parent 78f425de68
commit 2a966ac2a9
1 changed files with 7 additions and 7 deletions
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14
core/gas-model.c
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@ -6,7 +6,10 @@
#include "dive.h"
/* "Virial minus one" - the virial cubic form without the initial 1.0 */
#define virial_m1(C, x1, x2, x3) (C[0]*x1+C[1]*x2+C[2]*x3)
static double virial_m1(const double coeff[], double x)
{
return x*coeff[0] + x*x*coeff[1] + x*x*x*coeff[2];
}
/*
* Z = pV/nRT
@ -44,7 +47,6 @@ double gas_compressibility_factor(struct gasmix gas, double bar)
+5.33304543646e-11
};
int o2, he;
double x1, x2, x3;
double Z;
/*
@ -58,11 +60,9 @@ double gas_compressibility_factor(struct gasmix gas, double bar)
o2 = get_o2(gas);
he = get_he(gas);
x1 = bar; x2 = x1*x1; x3 = x2*x1;
Z = virial_m1(o2_coefficients, x1, x2, x3) * o2 +
virial_m1(he_coefficients, x1, x2, x3) * he +
virial_m1(n2_coefficients, x1, x2, x3) * (1000 - o2 - he);
Z = virial_m1(o2_coefficients, bar) * o2 +
virial_m1(he_coefficients, bar) * he +
virial_m1(n2_coefficients, bar) * (1000 - o2 - he);
/*
* We add the 1.0 at the very end - the linear mixing of the