shared: add safe_strtofloat()

This is for parsing multiple numbers from one weston.ini key, which
means I cannot use weston_config_section_get_double(). Also going to use
float type, which has less range than double.

Ironically, the tests fill likely fail on locales that do not use
period as the radix character.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

shared/string-helpers.h

@@ -73,6 +73,37 @@ safe_strtoint(const char *str, int32_t *value)
 	return true;
 }
 
+/** Convert a localized string to a single-precision floating point value
+ *
+ * \param str The string to parse. Leading whitespace is ignored,
+ * otherwise the string must be exactly a real number in the current locale.
+ * \param[out] value Pointer to store the result to on success.
+ * \return True on success. False on failure and errno set to
+ * either ERANGE (under- or overflow) or EINVAL (the string is not strictly
+ * a number).
+ */
+static inline bool
+safe_strtofloat(const char *str, float *value)
+{
+	float ret;
+	char *end;
+
+	assert(str != NULL);
+
+	errno = 0;
+	ret = strtof(str, &end);
+	if (errno != 0) {
+		return false;
+	} else if (end == str || *end != '\0') {
+		errno = EINVAL;
+		return false;
+	}
+
+	*value = ret;
+
+	return true;
+}
+
 /**
  * Exactly like asprintf(), but sets *str_out to NULL if it fails.
  *

tests/string-test.c

@@ -88,3 +88,56 @@ TEST(strtol_conversions)
 
 	return RESULT_OK;
 }
+
+TEST(strtof_conversions)
+{
+	float val;
+
+	test_assert_true(safe_strtofloat("0.0", &val));
+	test_assert_f32_eq(val, 0.0);
+
+	test_assert_true(safe_strtofloat("-0.25", &val));
+	test_assert_f32_eq(val, -0.25);
+
+	test_assert_true(safe_strtofloat("  10", &val));
+	test_assert_f32_eq(val, 10.0);
+
+	test_assert_true(safe_strtofloat("+2.2e-4", &val));
+	test_assert_f32_eq(val, 2.2e-4);
+
+	test_assert_true(safe_strtofloat("3.3e3", &val));
+	test_assert_f32_eq(val, 3.3e3);
+
+	test_assert_true(safe_strtofloat("nan", &val));
+	test_assert_true(isnan(val));
+
+	test_assert_true(safe_strtofloat("inf", &val));
+	test_assert_f32_eq(val, HUGE_VALF);
+
+	test_assert_true(safe_strtofloat("-inf", &val));
+	test_assert_f32_eq(val, -HUGE_VALF);
+
+
+	test_assert_false(safe_strtofloat("", &val));
+	test_assert_int_eq(errno, EINVAL);
+
+	test_assert_false(safe_strtofloat("x", &val));
+	test_assert_int_eq(errno, EINVAL);
+
+	test_assert_false(safe_strtofloat("15k", &val));
+	test_assert_int_eq(errno, EINVAL);
+
+	test_assert_false(safe_strtofloat("b2.2", &val));
+	test_assert_int_eq(errno, EINVAL);
+
+	test_assert_false(safe_strtofloat("1.3f", &val));
+	test_assert_int_eq(errno, EINVAL);
+
+	test_assert_false(safe_strtofloat("1e-500", &val));
+	test_assert_int_eq(errno, ERANGE);
+
+	test_assert_false(safe_strtofloat("1e+500", &val));
+	test_assert_int_eq(errno, ERANGE);
+
+	return RESULT_OK;
+}