lib: kstrtox: add kstrtoudec64() and kstrtodec64()

Add helpers that parses decimal numbers into 64-bit number, i.e., decimal
point numbers with pre-defined scale are parsed into a 64-bit value (fixed
precision). After the decimal point, digits beyond the specified scale
are ignored.

Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

include/linux/kstrtox.h

@@ -97,6 +97,9 @@ int __must_check kstrtou8(const char *s, unsigned int base, u8 *res);
 int __must_check kstrtos8(const char *s, unsigned int base, s8 *res);
 int __must_check kstrtobool(const char *s, bool *res);
 
+int __must_check kstrtoudec64(const char *s, unsigned int scale, u64 *res);
+int __must_check kstrtodec64(const char *s, unsigned int scale, s64 *res);
+
 int __must_check kstrtoull_from_user(const char __user *s, size_t count, unsigned int base, unsigned long long *res);
 int __must_check kstrtoll_from_user(const char __user *s, size_t count, unsigned int base, long long *res);
 int __must_check kstrtoul_from_user(const char __user *s, size_t count, unsigned int base, unsigned long *res);

lib/kstrtox.c

@@ -17,6 +17,7 @@
 #include <linux/export.h>
 #include <linux/kstrtox.h>
 #include <linux/math64.h>
+#include <linux/overflow.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
 
@@ -394,6 +395,109 @@ int kstrtobool(const char *s, bool *res)
 }
 EXPORT_SYMBOL(kstrtobool);
 
+static int _kstrtoudec64(const char *s, unsigned int scale, u64 *res)
+{
+	unsigned int rv_int, rv_frac;
+	u64 _res = 0;
+
+	rv_int = _parse_integer(s, 10, &_res);
+	if (rv_int & KSTRTOX_OVERFLOW)
+		return -ERANGE;
+	s += rv_int;
+
+	if (*s == '.')
+		s++; /* skip decimal point */
+
+	rv_frac = _parse_integer(s, 10, &_res, scale, _res);
+	if (rv_frac & KSTRTOX_OVERFLOW)
+		return -ERANGE;
+	s += rv_frac;
+
+	/*
+	 * Check input beyond rv_int and rv_frac to cover cases like ".5" with
+	 * scale 0, which is considered a valid input, being parsed as 0.
+	 */
+	if (!rv_int && !rv_frac && !isdigit(*s))
+		return -EINVAL;
+
+	while (isdigit(*s)) /* truncate digits */
+		s++;
+
+	if (*s == '\n')
+		s++;
+	if (*s)
+		return -EINVAL;
+
+	if (_res && ((scale - rv_frac) > 19 /* log10(2^64) = 19.26 */ ||
+		     check_mul_overflow(_res, int_pow(10, scale - rv_frac), &_res)))
+		return -ERANGE;
+
+	*res = _res;
+	return 0;
+}
+
+/**
+ * kstrtoudec64() - Convert a string to an unsigned 64-bit scaled decimal value.
+ * @s: The start of the string. The string must be null-terminated, and may also
+ *  include a single newline before its terminating null. The first character
+ *  may also be a plus sign, but not a minus sign.
+ * @scale: The number of digits to the right of the decimal point.
+ * @res: Where to write the result of the conversion on success.
+ *
+ * For example, a scale of 3 with input "123.45" results in 123450. Note that
+ * trailing zeros in the fractional part input to match the scale are not
+ * required. Also, digits beyond the specified scale are ignored.
+ *
+ * Return: 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
+ */
+noinline
+int kstrtoudec64(const char *s, unsigned int scale, u64 *res)
+{
+	if (s[0] == '+')
+		s++;
+	return _kstrtoudec64(s, scale, res);
+}
+EXPORT_SYMBOL(kstrtoudec64);
+
+/**
+ * kstrtodec64() - Convert a string to a signed 64-bit scaled decimal value.
+ * @s: The start of the string. The string must be null-terminated, and may also
+ *  include a single newline before its terminating null. The first character
+ *  may also be a plus sign or a minus sign.
+ * @scale: The number of digits to the right of the decimal point.
+ * @res: Where to write the result of the conversion on success.
+ *
+ * For example, a scale of 4 with input "-3.141592" results in -31415. Note
+ * that digits beyond the specified scale are ignored. Also, trailing zeros in
+ * the fractional part input to match the scale are not required.
+ *
+ * Return: 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
+ */
+noinline
+int kstrtodec64(const char *s, unsigned int scale, s64 *res)
+{
+	u64 tmp;
+	int rv;
+
+	if (s[0] == '-') {
+		rv = _kstrtoudec64(s + 1, scale, &tmp);
+		if (rv < 0)
+			return rv;
+		if ((s64)-tmp > 0)
+			return -ERANGE;
+		*res = -tmp;
+	} else {
+		rv = kstrtoudec64(s, scale, &tmp);
+		if (rv < 0)
+			return rv;
+		if ((s64)tmp < 0)
+			return -ERANGE;
+		*res = tmp;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(kstrtodec64);
+
 /*
  * Since "base" would be a nonsense argument, this open-codes the
  * _from_user helper instead of using the helper macro below.