1 files changed, 74 insertions, 0 deletions
diff --git a/compiler-rt/lib/builtins/ppc/gcc_qsub.c b/compiler-rt/lib/builtins/ppc/gcc_qsub.c
new file mode 100644
index 000000000000..ac08120be0bd
--- /dev/null
+++ b/compiler-rt/lib/builtins/ppc/gcc_qsub.c
@@ -0,0 +1,74 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// long double __gcc_qsub(long double x, long double y);
+// This file implements the PowerPC 128-bit double-double add operation.
+// This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)
+
+#include "DD.h"
+
+long double __gcc_qsub(long double x, long double y) {
+  static const uint32_t infinityHi = UINT32_C(0x7ff00000);
+
+  DD dst = {.ld = x}, src = {.ld = y};
+
+  register double A = dst.s.hi, a = dst.s.lo, B = -src.s.hi, b = -src.s.lo;
+
+  // If both operands are zero:
+  if ((A == 0.0) && (B == 0.0)) {
+    dst.s.hi = A + B;
+    dst.s.lo = 0.0;
+    return dst.ld;
+  }
+
+  // If either operand is NaN or infinity:
+  const doublebits abits = {.d = A};
+  const doublebits bbits = {.d = B};
+  if ((((uint32_t)(abits.x >> 32) & infinityHi) == infinityHi) ||
+      (((uint32_t)(bbits.x >> 32) & infinityHi) == infinityHi)) {
+    dst.s.hi = A + B;
+    dst.s.lo = 0.0;
+    return dst.ld;
+  }
+
+  // If the computation overflows:
+  // This may be playing things a little bit fast and loose, but it will do for
+  // a start.
+  const double testForOverflow = A + (B + (a + b));
+  const doublebits testbits = {.d = testForOverflow};
+  if (((uint32_t)(testbits.x >> 32) & infinityHi) == infinityHi) {
+    dst.s.hi = testForOverflow;
+    dst.s.lo = 0.0;
+    return dst.ld;
+  }
+
+  double H, h;
+  double T, t;
+  double W, w;
+  double Y;
+
+  H = B + (A - (A + B));
+  T = b + (a - (a + b));
+  h = A + (B - (A + B));
+  t = a + (b - (a + b));
+
+  if (local_fabs(A) <= local_fabs(B))
+    w = (a + b) + h;
+  else
+    w = (a + b) + H;
+
+  W = (A + B) + w;
+  Y = (A + B) - W;
+  Y += w;
+
+  if (local_fabs(a) <= local_fabs(b))
+    w = t + Y;
+  else
+    w = T + Y;
+
+  dst.s.hi = Y = W + w;
+  dst.s.lo = (W - Y) + w;
+
+  return dst.ld;
+}