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diff --git a/sys/compat/linuxkpi/common/include/linux/math64.h b/sys/compat/linuxkpi/common/include/linux/math64.h
--- a/sys/compat/linuxkpi/common/include/linux/math64.h
+++ b/sys/compat/linuxkpi/common/include/linux/math64.h
@@ -108,6 +108,54 @@
return ((x / div) * y + (rem * y) / div);
}
+static inline uint64_t
+mul_u64_u64_div_u64(uint64_t x, uint64_t y, uint64_t z)
+{
+ uint64_t res, rem;
+ uint64_t x1, y1, y1z;
+
+ res = rem = 0;
+ x1 = x;
+ y1z = y / z;
+ y1 = y - y1z * z;
+
+ /*
+ * INVARIANT: x * y = res * z + rem + (y1 + y1z * z) * x1
+ * INVARIANT: y1 < z
+ * INVARIANT: rem < z
+ */
+ while (x1 > 0) {
+ /* Handle low bit. */
+ if (x1 & 1) {
+ x1 &= ~1;
+ res += y1z;
+ rem += y1;
+ if ((rem < y1) || (rem >= z)) {
+ res += 1;
+ rem -= z;
+ }
+ }
+
+ /* Shift x1 right and (y1 + y1z * z) left */
+ x1 >>= 1;
+ if ((y1 * 2 < y1) || (y1 * 2 >= z)) {
+ y1z = y1z * 2 + 1;
+ y1 = y1 * 2 - z;
+ } else {
+ y1z *= 2;
+ y1 *= 2;
+ }
+ }
+
+ KASSERT(res * z + rem == x * y, ("%s: res %ju * z %ju + rem %ju != "
+ "x %ju * y %ju", __func__, (uintmax_t)res, (uintmax_t)z,
+ (uintmax_t)rem, (uintmax_t)x, (uintmax_t)y));
+ KASSERT(rem < z, ("%s: rem %ju >= z %ju\n", __func__,
+ (uintmax_t)rem, (uintmax_t)z);
+
+ return (res);
+}
+
static inline uint64_t
mul_u64_u32_shr(uint64_t x, uint32_t y, unsigned int shift)
{

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