compat: Add libcomparetf2 shim

Provide __lttf2 to various blobs

Change-Id: Idb8309fcdc969e9954f0b8b4ca7a39ab261e64de

Android.bp

@@ -359,3 +359,10 @@ cc_library_shared {
     system_ext_specific: true,
     vendor_available: true,
 }
+
+cc_library_shared {
+    name: "libcomparetf2_shim",
+    srcs: ["libcomparetf2/comparetf2.c"],
+    compile_multilib: "64",
+    vendor: true,
+}

libcomparetf2/comparetf2.c

@@ -0,0 +1,71 @@
+//===-- lib/comparetf2.c - Quad-precision comparisons -------------*- C -*-===//
+//
+// 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
+
+#include <limits.h>
+
+typedef __uint128_t rep_t;
+typedef __int128_t srep_t;
+typedef long double fp_t;
+
+#define REP_C (__uint128_t)
+#define typeWidth (sizeof(rep_t) * CHAR_BIT)
+#define significandBits 112
+#define exponentBits (typeWidth - significandBits - 1)
+
+#define implicitBit (REP_C(1) << significandBits)
+#define significandMask (implicitBit - 1U)
+#define signBit (REP_C(1) << (significandBits + exponentBits))
+#define absMask (signBit - 1U)
+#define exponentMask (absMask ^ significandMask)
+#define infRep exponentMask
+
+static __inline rep_t toRep(fp_t x) {
+  const union {
+    fp_t f;
+    rep_t i;
+  } rep = {.f = x};
+  return rep.i;
+}
+
+enum LE_RESULT { LE_LESS = -1, LE_EQUAL = 0, LE_GREATER = 1, LE_UNORDERED = 1 };
+
+enum LE_RESULT __lttf2(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;
+  } else {
+    // 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).
+    if (aInt > bInt)
+      return LE_LESS;
+    else if (aInt == bInt)
+      return LE_EQUAL;
+    else
+      return LE_GREATER;
+  }
+}