1 files changed, 74 insertions, 0 deletions
diff --git a/lib/ppc/gcc_qsub.c b/lib/ppc/gcc_qsub.c
new file mode 100644
index 000000000..f77deaa4f
--- /dev/null
+++ b/lib/ppc/gcc_qsub.c
@@ -0,0 +1,74 @@
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+
+// 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.hi, a =  dst.lo,
+					B = -src.hi, b = -src.lo;
+	
+	// If both operands are zero:
+	if ((A == 0.0) && (B == 0.0)) {
+		dst.hi = A + B;
+		dst.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.hi = A + B;
+		dst.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.hi = testForOverflow;
+		dst.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 (fabs(A) <= fabs(B))
+		w = (a + b) + h;
+	else
+		w = (a + b) + H;
+	
+	W = (A + B) + w;
+	Y = (A + B) - W;
+	Y += w;
+	
+	if (fabs(a) <= fabs(b))
+		w = t + Y;
+	else
+		w = T + Y;
+	
+	dst.hi = Y = W + w;
+	dst.lo = (W - Y) + w;
+	
+	return dst.ld;
+}