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diff --git a/runtime/c/i64_dtos.c b/runtime/c/i64_dtos.c
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+/*****************************************************************
+ *
+ *               The Compcert verified compiler
+ *
+ *           Xavier Leroy, INRIA Paris-Rocquencourt
+ *
+ * Copyright (c) 2013 Institut National de Recherche en Informatique et
+ *  en Automatique.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the <organization> nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT
+ * HOLDER> BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ **********************************************************************/
+
+/* Helper functions for 64-bit integer arithmetic. Reference C implementation */
+
+#include "i64.h"
+
+/* Conversion float64 -> signed int64 */
+
+long long __i64_dtos(double d)
+{
+  /* Extract bits of d's representation */
+  union { double d; unsigned long long i; } buf;
+  buf.d = d;
+  unsigned int h = buf.i >> 32;
+  /* Extract unbiased exponent */
+  int e = ((h & 0x7FF00000) >> 20) - (1023 + 52);
+  /* Check range of exponent */
+  if (e < -52) {
+    /* |d| is less than 1.0 */
+    return 0LL;
+  }
+  if (e >= 63 - 52) {
+    /* |d| is greater or equal to 2^63 */
+    if ((int) h < 0)
+      return -0x8000000000000000LL; /* min signed long long */
+    else
+      return  0x7FFFFFFFFFFFFFFFLL; /* max signed long long */
+  }
+  /* Extract true mantissa */
+  unsigned long long m =
+    (buf.i & ~0xFFF0000000000000LL) | 0x0010000000000000LL;
+  /* Shift it appropriately */
+  if (e >= 0)
+    m = __i64_shl(m, e);
+  else
+    m = __i64_shr(m, -e);
+  /* Apply sign to result */
+  if ((int) h < 0)
+    return -m;
+  else
+    return m;
+}