[APInt] Add helpers for rounding u/sdivs.

Reviewers: sanjoy, craig.topper

Subscribers: jlebar, hiraditya, bixia, llvm-commits

Differential Revision: https://reviews.llvm.org/D48498

llvm-svn: 335557

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 2c2ce9588a2..8be903f2ccb 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -2658,3 +2658,49 @@ void APInt::tcSetLeastSignificantBits(WordType *dst, unsigned parts,
   while (i < parts)
     dst[i++] = 0;
 }
+
+APInt llvm::APIntOps::RoundingUDiv(const APInt &A, const APInt &B,
+                                   APInt::Rounding RM) {
+  // Currently udivrem always rounds down.
+  switch (RM) {
+  case APInt::Rounding::DOWN:
+  case APInt::Rounding::TOWARD_ZERO:
+    return A.udiv(B);
+  case APInt::Rounding::UP: {
+    APInt Quo, Rem;
+    APInt::udivrem(A, B, Quo, Rem);
+    if (Rem == 0)
+      return Quo;
+    return Quo + 1;
+  }
+  }
+}
+
+APInt llvm::APIntOps::RoundingSDiv(const APInt &A, const APInt &B,
+                                   APInt::Rounding RM) {
+  switch (RM) {
+  case APInt::Rounding::DOWN:
+  case APInt::Rounding::UP: {
+    APInt Quo, Rem;
+    APInt::sdivrem(A, B, Quo, Rem);
+    if (Rem == 0)
+      return Quo;
+    // This algorithm deals with arbitrary rounding mode used by sdivrem.
+    // We want to check whether the non-integer part of the mathematical value
+    // is negative or not. If the non-integer part is negative, we need to round
+    // down from Quo; otherwise, if it's positive or 0, we return Quo, as it's
+    // already rounded down.
+    if (RM == APInt::Rounding::DOWN) {
+      if (Rem.isNegative() != B.isNegative())
+        return Quo - 1;
+      return Quo;
+    }
+    if (Rem.isNegative() != B.isNegative())
+      return Quo;
+    return Quo + 1;
+  }
+  // Currently sdiv rounds twards zero.
+  case APInt::Rounding::TOWARD_ZERO:
+    return A.sdiv(B);
+  }
+}