[APInt] Implement tcDecrement as a counterpart to tcIncrement. This is for use in APFloat IEEE-754R 2008 nextUp/nextDown function.
rdar://13852078
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182801 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 71c5095..108675d 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -2888,6 +2888,20 @@
return i == parts;
}
+/* Decrement a bignum in-place, return the borrow flag. */
+integerPart
+APInt::tcDecrement(integerPart *dst, unsigned int parts) {
+ for (unsigned int i = 0; i < parts; i++) {
+ // If the current word is non-zero, then the decrement has no effect on the
+ // higher-order words of the integer and no borrow can occur. Exit early.
+ if (dst[i]--)
+ return 0;
+ }
+ // If every word was zero, then there is a borrow.
+ return 1;
+}
+
+
/* Set the least significant BITS bits of a bignum, clear the
rest. */
void