[PATCH v10 02/11] lib: kstrtox: add kstrtoudec64() and kstrtodec64()

Rodrigo Alencar via B4 Relay
2026-04-15T09:52:18Z

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>
---
include/linux/kstrtox.h | 3 ++
lib/kstrtox.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 108 insertions(+)

diff --git a/include/linux/kstrtox.h b/include/linux/kstrtox.h
index 6ea897222af1..bec2fc17bde0 100644
--- a/include/linux/kstrtox.h
+++ b/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);
diff --git a/lib/kstrtox.c b/lib/kstrtox.c
index 97be2a39f537..c7625ba4ac88 100644
--- a/lib/kstrtox.c
+++ b/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>

@@ -392,6 +393,110 @@ int kstrtobool(const char *s, bool *res)
}
EXPORT_SYMBOL(kstrtobool);

+static int _kstrtoudec64(const char *s, unsigned int scale, u64 *res)
+{
+ u64 _res = 0, _frac = 0;
+ unsigned int rv;
+
+ if (scale > 19) /* log10(2^64) = 19.26 */
+ return -EINVAL;
+
+ if (*s != '.') {
+ rv = _parse_integer(s, 10, &_res);
+ if (rv & KSTRTOX_OVERFLOW)
+ return -ERANGE;
+ if (rv == 0)
+ return -EINVAL;
+ s += rv;
+ }
+
+ if (*s == '.' && scale) {
+ s++; /* skip decimal point */
+ rv = _parse_integer_limit(s, 10, &_frac, scale);
+ if (rv & KSTRTOX_OVERFLOW)
+ return -ERANGE;
+ if (rv == 0)
+ return -EINVAL;
+ s += rv;
+ if (rv < scale)
+ _frac *= int_pow(10, scale - rv);
+ while (isdigit(*s)) /* truncate */
+ s++;
+ }
+
+ if (*s == '\n')
+ s++;
+ if (*s)
+ return -EINVAL;
+
+ if (check_mul_overflow(_res, int_pow(10, scale), &_res) ||
+ check_add_overflow(_res, _frac, &_res))
+ return -ERANGE;
+
+ *res = _res;
+ return 0;
+}
+
+/**
+ * kstrtoudec64 - convert a string to an unsigned 64-bit decimal number
+ * @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. Digits beyond the specified
+ * scale are ignored.
+ * @scale: The number of digits to the right of the decimal point. For example,
+ * a scale of 2 would mean the number is represented with two decimal places,
+ * so "123.45" would be represented as 12345.
+ * @res: Where to write the result of the conversion on success.
+ *
+ * Returns 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 decimal number
+ * @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. Digits beyond the specified
+ * scale are ignored.
+ * @scale: The number of digits to the right of the decimal point. For example,
+ * a scale of 5 would mean the number is represented with five decimal places,
+ * so "-3.141592" would be represented as -314159.
+ * @res: Where to write the result of the conversion on success.
+ *
+ * Returns 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.

--
2.43.0