fdlibm: reduce accuracy slightly in favor of performance.

src/rempio2.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // ====================================================
 // Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 //
 // Developed at SunSoft, a Sun Microsystems, Inc. business.
 // Permission to use, copy, modify, and distribute this
 // software is freely granted, provided that this notice
@@ skipping 160 matching lines @@
 
   double fq[10];
   for (int i = jz; i >= 0; i--) {
     fw = 0.0;
     for (int k = 0; k <= jk && k <= jz - i; k++) fw += PIo2[k] * q[i + k];
     fq[jz - i] = fw;
   }
 
   fw = 0.0;
   for (int i = jz; i >= 0; i--) fw += fq[i];
-  y[0] = (ih == 0) ? fw : -fw;
-  fw = fq[0] - fw;
-  for (int i = 1; i <= jz; i++) fw += fq[i];
-  y[1] = (ih == 0) ? fw : -fw;
+  *y = (ih == 0) ? fw : -fw;
   return n & 7;
 }
 
 
 int rempio2(double x, double* y) {
   int32_t hx = static_cast<int32_t>(double_to_uint64(x) >> 32);
   int32_t ix = hx & 0x7fffffff;
 
   ASSERT(ix > 0x413921fb);  // Handling of lower ix has been omitted.
 
   int32_t e0 = (ix >> 20) - 1046;
   uint64_t zi = double_to_uint64(x) & 0xFFFFFFFFu;
   zi |= static_cast<uint64_t>(ix - (e0 << 20)) << 32;
   double z = uint64_to_double(zi);
 
   double tx[3];
   for (int i = 0; i < 2; i++) {
     tx[i] = static_cast<double>(static_cast<int32_t>(z));
     z = (z - tx[i]) * two24;
   }
   tx[2] = z;
 
   int nx = 3;
   while (tx[nx - 1] == zero) nx--;
   int n = __kernel_rem_pio2(tx, y, e0, nx);
   if (hx < 0) {
-    y[0] = -y[0];
-    y[1] = -y[1];
+    *y = -*y;
     return -n;
   }
   return n;
 }
 
 } }  // namespace v8::internal