Move helper functions for optimizing division by constant into the APInt
class.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70488 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 8ac589c..e77fcdb 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -1435,6 +1435,98 @@
return t[i].isNegative() ? t[i] + modulo : t[i];
}
+/// Calculate the magic numbers required to implement a signed integer division
+/// by a constant as a sequence of multiplies, adds and shifts. Requires that
+/// the divisor not be 0, 1, or -1. Taken from "Hacker's Delight", Henry S.
+/// Warren, Jr., chapter 10.
+APInt::ms APInt::magic() const {
+ const APInt& d = *this;
+ unsigned p;
+ APInt ad, anc, delta, q1, r1, q2, r2, t;
+ APInt allOnes = APInt::getAllOnesValue(d.getBitWidth());
+ APInt signedMin = APInt::getSignedMinValue(d.getBitWidth());
+ APInt signedMax = APInt::getSignedMaxValue(d.getBitWidth());
+ struct ms mag;
+
+ ad = d.abs();
+ t = signedMin + (d.lshr(d.getBitWidth() - 1));
+ anc = t - 1 - t.urem(ad); // absolute value of nc
+ p = d.getBitWidth() - 1; // initialize p
+ q1 = signedMin.udiv(anc); // initialize q1 = 2p/abs(nc)
+ r1 = signedMin - q1*anc; // initialize r1 = rem(2p,abs(nc))
+ q2 = signedMin.udiv(ad); // initialize q2 = 2p/abs(d)
+ r2 = signedMin - q2*ad; // initialize r2 = rem(2p,abs(d))
+ do {
+ p = p + 1;
+ q1 = q1<<1; // update q1 = 2p/abs(nc)
+ r1 = r1<<1; // update r1 = rem(2p/abs(nc))
+ if (r1.uge(anc)) { // must be unsigned comparison
+ q1 = q1 + 1;
+ r1 = r1 - anc;
+ }
+ q2 = q2<<1; // update q2 = 2p/abs(d)
+ r2 = r2<<1; // update r2 = rem(2p/abs(d))
+ if (r2.uge(ad)) { // must be unsigned comparison
+ q2 = q2 + 1;
+ r2 = r2 - ad;
+ }
+ delta = ad - r2;
+ } while (q1.ule(delta) || (q1 == delta && r1 == 0));
+
+ mag.m = q2 + 1;
+ if (d.isNegative()) mag.m = -mag.m; // resulting magic number
+ mag.s = p - d.getBitWidth(); // resulting shift
+ return mag;
+}
+
+/// Calculate the magic numbers required to implement an unsigned integer
+/// division by a constant as a sequence of multiplies, adds and shifts.
+/// Requires that the divisor not be 0. Taken from "Hacker's Delight", Henry
+/// S. Warren, Jr., chapter 10.
+APInt::mu APInt::magicu() const {
+ const APInt& d = *this;
+ unsigned p;
+ APInt nc, delta, q1, r1, q2, r2;
+ struct mu magu;
+ magu.a = 0; // initialize "add" indicator
+ APInt allOnes = APInt::getAllOnesValue(d.getBitWidth());
+ APInt signedMin = APInt::getSignedMinValue(d.getBitWidth());
+ APInt signedMax = APInt::getSignedMaxValue(d.getBitWidth());
+
+ nc = allOnes - (-d).urem(d);
+ p = d.getBitWidth() - 1; // initialize p
+ q1 = signedMin.udiv(nc); // initialize q1 = 2p/nc
+ r1 = signedMin - q1*nc; // initialize r1 = rem(2p,nc)
+ q2 = signedMax.udiv(d); // initialize q2 = (2p-1)/d
+ r2 = signedMax - q2*d; // initialize r2 = rem((2p-1),d)
+ do {
+ p = p + 1;
+ if (r1.uge(nc - r1)) {
+ q1 = q1 + q1 + 1; // update q1
+ r1 = r1 + r1 - nc; // update r1
+ }
+ else {
+ q1 = q1+q1; // update q1
+ r1 = r1+r1; // update r1
+ }
+ if ((r2 + 1).uge(d - r2)) {
+ if (q2.uge(signedMax)) magu.a = 1;
+ q2 = q2+q2 + 1; // update q2
+ r2 = r2+r2 + 1 - d; // update r2
+ }
+ else {
+ if (q2.uge(signedMin)) magu.a = 1;
+ q2 = q2+q2; // update q2
+ r2 = r2+r2 + 1; // update r2
+ }
+ delta = d - 1 - r2;
+ } while (p < d.getBitWidth()*2 &&
+ (q1.ult(delta) || (q1 == delta && r1 == 0)));
+ magu.m = q2 + 1; // resulting magic number
+ magu.s = p - d.getBitWidth(); // resulting shift
+ return magu;
+}
+
/// Implementation of Knuth's Algorithm D (Division of nonnegative integers)
/// from "Art of Computer Programming, Volume 2", section 4.3.1, p. 272. The
/// variables here have the same names as in the algorithm. Comments explain