[PATCH] {COMPILER-RT] Implement long double comparison functions

[GuanHong Liu]

The following functions are implemented:
__letf2, __gttf2, __netf2, __getf2, __eqtf2, __lttf2, __unordtf2

http://llvm-reviews.chandlerc.com/D2797

Files:
  lib/comparetf2.c

Index: lib/comparetf2.c
===================================================================
--- /dev/null
+++ lib/comparetf2.c
@@ -0,0 +1,131 @@
+//===-- lib/comparetf2.c - Quad-precision comparisons -------------*- C -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// // This file implements the following soft-float comparison routines:
+//
+//   __eqtf2   __getf2   __unordtf2
+//   __letf2   __gttf2
+//   __lttf2
+//   __netf2
+//
+// The semantics of the routines grouped in each column are identical, so there
+// is a single implementation for each, and wrappers to provide the other names.
+//
+// The main routines behave as follows:
+//
+//   __letf2(a,b) returns -1 if a < b
+//                         0 if a == b
+//                         1 if a > b
+//                         1 if either a or b is NaN
+//
+//   __getf2(a,b) returns -1 if a < b
+//                         0 if a == b
+//                         1 if a > b
+//                        -1 if either a or b is NaN
+//
+//   __unordtf2(a,b) returns 0 if both a and b are numbers
+//                           1 if either a or b is NaN
+//
+// Note that __letf2( ) and __getf2( ) are identical except in their handling of
+// NaN values.
+//
+//===----------------------------------------------------------------------===//
+
+#define QUAD_PRECISION
+#include "fp_lib.h"
+
+enum LE_RESULT {
+    LE_LESS      = -1,
+    LE_EQUAL     =  0,
+    LE_GREATER   =  1,
+    LE_UNORDERED =  1
+};
+
+enum LE_RESULT __letf2(fp_t a, fp_t b) {
+
+    const srep_t aInt = toRep(a);
+    const srep_t bInt = toRep(b);
+    const rep_t aAbs = aInt & absMask;
+    const rep_t bAbs = bInt & absMask;
+
+    // If either a or b is NaN, they are unordered.
+    if (aAbs > infRep || bAbs > infRep) return LE_UNORDERED;
+
+    // If a and b are both zeros, they are equal.
+    if ((aAbs | bAbs) == 0) return LE_EQUAL;
+
+    // If at least one of a and b is positive, we get the same result comparing
+    // a and b as signed integers as we would with a floating-point compare.
+    if ((aInt & bInt) >= 0) {
+        if (aInt < bInt) return LE_LESS;
+        else if (aInt == bInt) return LE_EQUAL;
+        else return LE_GREATER;
+    }
+
+    // Otherwise, both are negative, so we need to flip the sense of the
+    // comparison to get the correct result.  (This assumes a twos- or ones-
+    // complement integer representation; if integers are represented in a
+    // sign-magnitude representation, then this flip is incorrect).
+    else {
+        if (aInt > bInt) return LE_LESS;
+        else if (aInt == bInt) return LE_EQUAL;
+        else return LE_GREATER;
+    }
+}
+
+enum GE_RESULT {
+    GE_LESS      = -1,
+    GE_EQUAL     =  0,
+    GE_GREATER   =  1,
+    GE_UNORDERED = -1   // Note: different from LE_UNORDERED
+};
+
+enum GE_RESULT __getf2(fp_t a, fp_t b) {
+
+    const srep_t aInt = toRep(a);
+    const srep_t bInt = toRep(b);
+    const rep_t aAbs = aInt & absMask;
+    const rep_t bAbs = bInt & absMask;
+
+    if (aAbs > infRep || bAbs > infRep) return GE_UNORDERED;
+    if ((aAbs | bAbs) == 0) return GE_EQUAL;
+    if ((aInt & bInt) >= 0) {
+        if (aInt < bInt) return GE_LESS;
+        else if (aInt == bInt) return GE_EQUAL;
+        else return GE_GREATER;
+    } else {
+        if (aInt > bInt) return GE_LESS;
+        else if (aInt == bInt) return GE_EQUAL;
+        else return GE_GREATER;
+    }
+}
+
+int __unordtf2(fp_t a, fp_t b) {
+    const rep_t aAbs = toRep(a) & absMask;
+    const rep_t bAbs = toRep(b) & absMask;
+    return aAbs > infRep || bAbs > infRep;
+}
+
+// The following are alternative names for the preceeding routines.
+
+enum LE_RESULT __eqtf2(fp_t a, fp_t b) {
+    return __letf2(a, b);
+}
+
+enum LE_RESULT __lttf2(fp_t a, fp_t b) {
+    return __letf2(a, b);
+}
+
+enum LE_RESULT __netf2(fp_t a, fp_t b) {
+    return __letf2(a, b);
+}
+
+enum GE_RESULT __gttf2(fp_t a, fp_t b) {
+    return __getf2(a, b);
+}
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