r223175 - Intrin: Add _umul128

David Majnemer david.majnemer at gmail.com
Tue Dec 2 15:30:24 PST 2014

Author: majnemer
Date: Tue Dec  2 17:30:24 2014
New Revision: 223175

URL: http://llvm.org/viewvc/llvm-project?rev=223175&view=rev
Intrin: Add _umul128

Implement _umul128; it provides the high and low halves of a 128-bit
multiply.  We can simply use our __int128 arithmetic to implement this,
we generate great code for it:
        movq    %rdx, %rax
        mulq    %rcx
        movq    %rdx, (%r8)

Differential Revision: http://reviews.llvm.org/D6486


Modified: cfe/trunk/lib/Headers/Intrin.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Headers/Intrin.h?rev=223175&r1=223174&r2=223175&view=diff
--- cfe/trunk/lib/Headers/Intrin.h (original)
+++ cfe/trunk/lib/Headers/Intrin.h Tue Dec  2 17:30:24 2014
@@ -417,9 +417,18 @@ int __cdecl _setjmpex(jmp_buf);
 unsigned __int64 _shlx_u64(unsigned __int64, unsigned int);
 unsigned __int64 shrx_u64(unsigned __int64, unsigned int);
-unsigned __int64 _umul128(unsigned __int64 _Multiplier,
-                          unsigned __int64 _Multiplicand,
-                          unsigned __int64 *_HighProduct);
+ * Multiply two 64-bit integers and obtain a 64-bit result.
+ * The low-half is returned directly and the high half is in an out parameter.
+ */
+static __inline__ unsigned __int64 __attribute__((__always_inline__, __nodebug__))
+_umul128(unsigned __int64 _Multiplier, unsigned __int64 _Multiplicand,
+         unsigned __int64 *_HighProduct) {
+  unsigned __int128 _FullProduct =
+      (unsigned __int128)_Multiplier * (unsigned __int128)_Multiplicand;
+  *_HighProduct = FullProduct >> 64;
+  return FullProduct;
 void __cdecl _xrstor64(void const *, unsigned __int64);
 void __cdecl _xsave64(void *, unsigned __int64);
 void __cdecl _xsaveopt64(void *, unsigned __int64);

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