[libc-commits] [PATCH] D140070: [libc] fix shifting exact multiples of 64 in uint

[Michael Jones via Phabricator via libc-commits]

michaelrj updated this revision to Diff 483262.
michaelrj marked 2 inline comments as done.
michaelrj added a comment.

move check for shift of 0 outside of loop for shift_left
remove redundant check in shift right


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140070/new/

https://reviews.llvm.org/D140070

Files:
  libc/src/__support/UInt.h
  libc/test/src/__support/uint_test.cpp


Index: libc/test/src/__support/uint_test.cpp
===================================================================
--- libc/test/src/__support/uint_test.cpp
+++ libc/test/src/__support/uint_test.cpp
@@ -326,6 +326,10 @@
   LL_UInt128 result6({0, 0});
   EXPECT_EQ((val2 << 128), result6);
   EXPECT_EQ((val2 << 256), result6);
+
+  LL_UInt192 val3({1, 0, 0});
+  LL_UInt192 result7({0, 1, 0});
+  EXPECT_EQ((val3 << 64), result7);
 }
 
 TEST(LlvmLibcUIntClassTest, ShiftRightTests) {
@@ -363,6 +367,10 @@
   EXPECT_EQ((v2 >> 64), r2);
   EXPECT_EQ((v2 >> 128), r3);
   EXPECT_EQ((r2 >> 64), r3);
+
+  LL_UInt192 val3({0, 0, 1});
+  LL_UInt192 result7({0, 1, 0});
+  EXPECT_EQ((val3 >> 64), result7);
 }
 
 TEST(LlvmLibcUIntClassTest, AndTests) {
Index: libc/src/__support/UInt.h
===================================================================
--- libc/src/__support/UInt.h
+++ libc/src/__support/UInt.h
@@ -364,7 +364,7 @@
       val[1] = uint64_t(tmp >> 64);
       return;
     }
-#endif                           // __SIZEOF_INT128__
+#endif // __SIZEOF_INT128__
     if (unlikely(s == 0))
       return;
 
@@ -374,11 +374,17 @@
 
     if (drop < WordCount) {
       i = WordCount - 1;
-      size_t j = WordCount - 1 - drop;
-      for (; j > 0; --i, --j) {
-        val[i] = (val[j] << shift) | (val[j - 1] >> (64 - shift));
+      if (shift > 0) {
+        for (size_t j = WordCount - 1 - drop; j > 0; --i, --j) {
+          val[i] = (val[j] << shift) | (val[j - 1] >> (64 - shift));
+        }
+        val[i] = val[0] << shift;
+      } else {
+        for (size_t j = WordCount - 1 - drop; j > 0; --i, --j) {
+          val[i] = val[j];
+        }
+        val[i] = val[0];
       }
-      val[i] = val[0] << shift;
     }
 
     for (size_t j = 0; j < i; ++j) {


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D140070.483262.patch
Type: text/x-patch
Size: 1774 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/libc-commits/attachments/20221215/75e6c838/attachment-0001.bin>