core: convert strtod.c to C++

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

core/strtod.cpp

@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Sane helper for 'strtod()'.
+ *
+ * Sad that we even need this, but the C library version has
+ * insane locale behavior, and while the Qt "toDouble()" routines
+ * are better in that regard, they don't have an end pointer
+ * (having replaced it with the completely idiotic "ok" boolean
+ * pointer instead).
+ *
+ * So if you want the C locale kind of parsing, use the
+ * ascii_strtod() function. But if you want a more relaxed
+ * "Hey, Europeans are people too, even if they have locales
+ * with commas", use general_strtod() instead.
+ */
+#include <ctype.h>
+#include "subsurface-string.h"
+
+static double strtod_flags(const char *str, const char **ptr, bool no_comma)
+{
+	char c;
+	const char *p = str, *ep;
+	double val = 0.0;
+	double decimal = 1.0;
+	bool sign = false, esign = false;
+	bool numbers = false, dot = false;
+
+	/* skip spaces */
+	while (isspace(c = *p++))
+		/* */;
+
+	/* optional sign */
+	switch (c) {
+	case '-':
+		sign = true;
+	/* fallthrough */
+	case '+':
+		c = *p++;
+	}
+
+	/* Mantissa */
+	for (;; c = *p++) {
+		if (c == '.' || (c == ',' && !no_comma)) {
+			if (dot)
+				goto done;
+			dot = true;
+			continue;
+		}
+		if (c >= '0' && c <= '9') {
+			numbers = true;
+			val = (val * 10) + (c - '0');
+			if (dot)
+				decimal *= 10;
+			continue;
+		}
+		if (c != 'e' && c != 'E')
+			goto done;
+		break;
+	}
+
+	if (!numbers)
+		goto done;
+
+	/* Exponent */
+	ep = p;
+	c = *ep++;
+	switch (c) {
+	case '-':
+		esign = true;
+	/* fallthrough */
+	case '+':
+		c = *ep++;
+	}
+
+	if (c >= '0' && c <= '9') {
+		p = ep;
+		int exponent = c - '0';
+
+		for (;;) {
+			c = *p++;
+			if (c < '0' || c > '9')
+				break;
+			exponent *= 10;
+			exponent += c - '0';
+		}
+
+		/* We're not going to bother playing games */
+		if (exponent > 308)
+			exponent = 308;
+
+		while (exponent-- > 0) {
+			if (esign)
+				decimal *= 10;
+			else
+				decimal /= 10;
+		}
+	}
+
+done:
+	if (!numbers)
+		goto no_conversion;
+	if (ptr)
+		*ptr = p - 1;
+	return (sign ? -val : val) / decimal;
+
+no_conversion:
+	if (ptr)
+		*ptr = str;
+	return 0.0;
+}
+
+extern "C" double permissive_strtod(const char *str, const char **ptr)
+{
+	return strtod_flags(str, ptr, false);
+}
+
+extern "C" double ascii_strtod(const char *str, const char **ptr)
+{
+	return strtod_flags(str, ptr, true);
+}