[PATCH v10 04/11] lib: math: div64: add div64_s64_rem()

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

Add div64_s64_rem() function, with 32-bit implementation that uses
div64_u64_rem() and a branchless approach to resolve the sign of the
remainder and quotient (negation in two's complement).

Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
---
include/linux/math64.h | 18 ++++++++++++++++++
lib/math/div64.c | 15 +++++++++++++++
2 files changed, 33 insertions(+)

diff --git a/include/linux/math64.h b/include/linux/math64.h
index cc305206d89f..99189410d4bb 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -57,6 +57,20 @@ static inline u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
return dividend / divisor;
}

+/**
+ * div64_s64_rem - signed 64bit divide with 64bit divisor and remainder
+ * @dividend: signed 64bit dividend
+ * @divisor: signed 64bit divisor
+ * @remainder: pointer to signed 64bit remainder
+ *
+ * Return: sets ``*remainder``, then returns dividend / divisor
+ */
+static inline s64 div64_s64_rem(s64 dividend, s64 divisor, s64 *remainder)
+{
+ *remainder = dividend % divisor;
+ return dividend / divisor;
+}
+
/**
* div64_u64 - unsigned 64bit divide with 64bit divisor
* @dividend: unsigned 64bit dividend
@@ -102,6 +116,10 @@ extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
extern u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder);
#endif

+#ifndef div64_s64_rem
+extern s64 div64_s64_rem(s64 dividend, s64 divisor, s64 *remainder);
+#endif
+
#ifndef div64_u64
extern u64 div64_u64(u64 dividend, u64 divisor);
#endif
diff --git a/lib/math/div64.c b/lib/math/div64.c
index d1e92ea24fce..0b10ded09a9b 100644
--- a/lib/math/div64.c
+++ b/lib/math/div64.c
@@ -158,6 +158,21 @@ u64 div64_u64(u64 dividend, u64 divisor)
EXPORT_SYMBOL(div64_u64);
#endif

+#ifndef div64_s64_rem
+s64 div64_s64_rem(s64 dividend, s64 divisor, s64 *remainder)
+{
+ s64 quot, t, rem;
+
+ quot = div64_u64_rem(abs(dividend), abs(divisor), (u64 *)&rem);
+ t = dividend >> 63;
+ *remainder = (rem ^ t) - t;
+ t = (dividend ^ divisor) >> 63;
+
+ return (quot ^ t) - t;
+}
+EXPORT_SYMBOL(div64_s64_rem);
+#endif
+
#ifndef div64_s64
s64 div64_s64(s64 dividend, s64 divisor)
{

--
2.43.0