[Xen-devel] [PATCH v4 05/10] x86: Add functions for 64-bit integer arithmetic

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

This patch adds several functions to take multiplication, division and
shifting involving 64-bit integers.

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
Changes in v4:
 (addressing Jan Beulich's comments)
 * Rewrite mul_u64_u64_shr() in assembly.

 xen/include/asm-x86/math64.h | 47 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 xen/include/asm-x86/math64.h

diff --git a/xen/include/asm-x86/math64.h b/xen/include/asm-x86/math64.h
new file mode 100644
index 0000000..2ddec62
--- /dev/null
+++ b/xen/include/asm-x86/math64.h
@@ -0,0 +1,47 @@
+#ifndef __X86_MATH64
+#define __X86_MATH64
+
+/*
+ * (a * mul) / divisor
+ *
+ * This function is derived from Linux kernel
+ * (mul_u64_u32_div() in include/linux/math64.h)
+ */
+static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 divisor)
+{
+    union {
+        u64 ll;
+        struct {
+            u32 low, high;
+        } l;
+    } u, rl, rh;
+
+    u.ll = a;
+    rl.ll = (u64)u.l.low * mul;
+    rh.ll = (u64)u.l.high * mul + rl.l.high;
+
+    /* Bits 32-63 of the result will be in rh.l.low. */
+    rl.l.high = do_div(rh.ll, divisor);
+
+    /* Bits 0-31 of the result will be in rl.l.low. */
+    do_div(rl.ll, divisor);
+
+    rl.l.high = rh.l.low;
+    return rl.ll;
+}
+
+/*
+ * (a * mul) >> n
+ */
+static inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int n)
+{
+    u64 hi, lo;
+
+    asm volatile ( "mulq %2; shrdq %1,%0"
+                   : "=a" (lo), "=d" (hi)
+                   : "rm" (mul), "0" (a), "c" (n) );
+
+    return lo;
+}
+
+#endif
-- 
2.7.0


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