Unify float calulations: use double

Internal floating point (FP) calculations should be performed using double
unless there is a very good reason. This avoids headaches with conversions.
Indeed, the vast majority of FP calculations were already done using double.
This patch adapts most remaining calculations. Not converted where things
that were based on binary representations and variables which weren't used
anyway.

An analysis of all instances follows:

core/plannernotes.c, l.404:

This was a comparison between two floats. On the left side, first an integer
was cast to float then multiplied with and integer and divided by a constant
double. The right hand side was an integer cast to a float. Simply divide by
1000.0 first to convert to double and continue with calculations. On the right
hand side, remove the cast, because the integer will be implicitely cast to
double for comparison. This conversion actually emits less instructions,
because no conversion to double and back is performed.

core/planner.c, l.613:

Same analysis as previous case.

subsurface-desktop-main.cpp, l.155:

A local variable representing the version OpenGL version. Turn this into
integer logic. Not only does this avoid dreaded FP rounding issues, it also
works correctly for minor version > 10 (not that such a thing is to be
expected anytime soon).

abstractpreferenceswidget.[h/cpp]:

A widget where the position is described as a float. Turn into double.

desktop-widgets/divelogexportdialog.cpp, l.313:

total_weight is described as float. Use double arithmetics instead. This
instance fixes a truncation warning emitted by gcc.

core/planner.c

@@ -610,7 +610,7 @@ bool enough_gas(int current_cylinder)
 	if (!cyl->start.mbar)
 		return true;
 	if (cyl->type.size.mliter)
-		return (float)(cyl->end.mbar - prefs.reserve_gas) * cyl->type.size.mliter / 1000.0 > (float) cyl->deco_gas_used.mliter;
+		return (cyl->end.mbar - prefs.reserve_gas) / 1000.0 * cyl->type.size.mliter > cyl->deco_gas_used.mliter;
 	else
 		return true;
 }

core/plannernotes.c

@@ -401,8 +401,8 @@ void add_plan_to_notes(struct diveplan *diveplan, struct dive *dive, bool show_d
 					translate("gettextFromC", "Warning:"),
 					translate("gettextFromC", "this is more gas than available in the specified cylinder!"));
 			else
-				if ((float) cyl->end.mbar * cyl->type.size.mliter / 1000.0 / gas_compressibility_factor(&cyl->gasmix, cyl->end.mbar / 1000.0)
+				if (cyl->end.mbar / 1000.0 * cyl->type.size.mliter / gas_compressibility_factor(&cyl->gasmix, cyl->end.mbar / 1000.0)
-				    < (float) cyl->deco_gas_used.mliter)
+				    < cyl->deco_gas_used.mliter)
 					snprintf(warning, sizeof(warning), "<br>&nbsp;&mdash; <span style='color: red;'>%s </span> %s",
 						translate("gettextFromC", "Warning:"),
 						translate("gettextFromC", "not enough reserve for gas sharing on ascent!"));

desktop-widgets/divelogexportdialog.cpp

@@ -310,7 +310,7 @@ void DiveLogExportDialog::export_TeX(const char *filename, const bool selected_o
 		int i;
 		int qty_cyl;
 		int qty_weight;
-		float total_weight;
+		double total_weight;
 
 		if (need_pagebreak)
 			put_format(&buf, "\\vfill\\eject\n");

desktop-widgets/preferences/abstractpreferenceswidget.cpp

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "abstractpreferenceswidget.h"
 
-AbstractPreferencesWidget::AbstractPreferencesWidget(const QString& name, const QIcon& icon, float positionHeight)
+AbstractPreferencesWidget::AbstractPreferencesWidget(const QString& name, const QIcon& icon, double positionHeight)
 : QWidget(), _icon(icon), _name(name), _positionHeight(positionHeight)
 {
 }
@@ -16,7 +16,7 @@ QString AbstractPreferencesWidget::name() const
 	return _name;
 }
 
-float AbstractPreferencesWidget::positionHeight() const
+double AbstractPreferencesWidget::positionHeight() const
 {
 	return _positionHeight;
 }

desktop-widgets/preferences/abstractpreferenceswidget.h

@@ -8,10 +8,10 @@
 class AbstractPreferencesWidget : public QWidget {
 	Q_OBJECT
 public:
-	AbstractPreferencesWidget(const QString& name, const QIcon& icon, float positionHeight);
+	AbstractPreferencesWidget(const QString& name, const QIcon& icon, double positionHeight);
 	QIcon icon() const;
 	QString name() const;
-	float positionHeight() const;
+	double positionHeight() const;
 
 	/* gets the values from the preferences and should set the correct values in
 	 * the interface */
@@ -26,6 +26,6 @@ signals:
 private:
 	QIcon _icon;
 	QString _name;
-	float _positionHeight;
+	double _positionHeight;
 };
 #endif

subsurface-desktop-main.cpp

@@ -152,7 +152,6 @@ void validateGL()
 	QOffscreenSurface surface;
 	QOpenGLFunctions *func;
 	const char *verChar;
-	float verFloat;
 
 	surface.setFormat(ctx.format());
 	surface.create();
@@ -182,9 +181,10 @@ void validateGL()
 			 "before running Subsurface!\n").toUtf8().data();
 			 return;
 		}
-		if (sscanf(verChar, "%f", &verFloat) == 1) {
+		int min, maj;
-			verMajor = (GLint)verFloat;
+		if (sscanf(verChar, "%d.%d", &maj, &min) == 2) {
-			verMinor = (GLint)roundf((verFloat - verMajor) * 10.f);
+			verMajor = (GLint)maj;
+			verMinor = (GLint)min;
 		}
 	}
 	// attempt to detect version using the newer API