Cleanup: pass gasmix by value

In a previous commit, the get_gasmix_* functions were changed to
return by value. For consistency, also pass gasmix by value.

Note that on common 64-bit platforms struct gasmix is the size
of a pointer [2 * 32 bit vs. 64 bit] and therefore uses the
same space on the stack. On 32-bit platforms, the stack use
is probably doubled, but in return a dereference is avoided.

Supporting arbitrary gas-mixes (H2, Ar, ...) will be such an
invasive change that going back to pointers is probably the
least of our worries.

This commit is a step in const-ifying input parameters (passing
by value is the ultimate way of signaling that the input parameter
will not be changed [unless there are references to said parameter]).

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 4 insertions, 4 deletions

diff --git a/core/gas-model.c b/core/gas-model.c
index 49c677967..7fb9ce111 100644
--- a/core/gas-model.c
+++ b/core/gas-model.c
@@ -26,7 +26,7 @@
  * NOTE! Helium coefficients are a linear mix operation between the
  * 323K and one for 273K isotherms, to make everything be at 300K.
  */
-double gas_compressibility_factor(struct gasmix *gas, double bar)
+double gas_compressibility_factor(struct gasmix gas, double bar)
 {
 	static const double o2_coefficients[3] = {
 		-7.18092073703e-04,
@@ -69,15 +69,15 @@ double gas_compressibility_factor(struct gasmix *gas, double bar)
 /* Compute the new pressure when compressing (expanding) volome v1 at pressure p1 bar to volume v2
  * taking into account the compressebility (to first order) */
 
-double isothermal_pressure(struct gasmix *gas, double p1, int volume1, int volume2)
+double isothermal_pressure(struct gasmix gas, double p1, int volume1, int volume2)
 {
 	double p_ideal = p1 * volume1 / volume2 / gas_compressibility_factor(gas, p1);
 
 	return p_ideal * gas_compressibility_factor(gas, p_ideal);
 }
 
-inline double gas_density(struct gasmix *gas, int pressure) {
-	int density =  gas->he.permille * HE_DENSITY + gas->o2.permille * O2_DENSITY + (1000 - gas->he.permille - gas->o2.permille) * N2_DENSITY;
+inline double gas_density(struct gasmix gas, int pressure) {
+	int density =  gas.he.permille * HE_DENSITY + gas.o2.permille * O2_DENSITY + (1000 - gas.he.permille - gas.o2.permille) * N2_DENSITY;
 
 	return density * (double) pressure / gas_compressibility_factor(gas, pressure / 1000.0) / SURFACE_PRESSURE / 1000000.0;
 }