1 files changed, 86 insertions, 0 deletions
diff --git a/lib/floattidf.c b/lib/floattidf.c
new file mode 100644
index 000000000000..274f58517c4e
--- /dev/null
+++ b/lib/floattidf.c
@@ -0,0 +1,86 @@
+/* ===-- floattidf.c - Implement __floattidf -------------------------------===
+ *
+ *                    The LLVM Compiler Infrastructure
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __floattidf for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */ 
+
+#if __x86_64
+
+#include "int_lib.h"
+#include <float.h>
+
+/* Returns: convert a to a double, rounding toward even.*/
+
+/* Assumption: double is a IEEE 64 bit floating point type 
+ *            ti_int is a 128 bit integral type
+ */
+
+/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 
+
+si_int __clzti2(ti_int a);
+
+double
+__floattidf(ti_int a)
+{
+    if (a == 0)
+        return 0.0;
+    const unsigned N = sizeof(ti_int) * CHAR_BIT;
+    const ti_int s = a >> (N-1);
+    a = (a ^ s) - s;
+    int sd = N - __clzti2(a);  /* number of significant digits */
+    int e = sd - 1;             /* exponent */
+    if (sd > DBL_MANT_DIG)
+    {
+        /* start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
+         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
+         *                                               12345678901234567890123456
+         * 1 = msb 1 bit
+         * P = bit DBL_MANT_DIG-1 bits to the right of 1
+         * Q = bit DBL_MANT_DIG bits to the right of 1
+         * R = "or" of all bits to the right of Q
+         */
+        switch (sd)
+        {
+        case DBL_MANT_DIG + 1:
+            a <<= 1;
+            break;
+        case DBL_MANT_DIG + 2:
+            break;
+        default:
+            a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) |
+                ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
+        };
+        /* finish: */
+        a |= (a & 4) != 0;  /* Or P into R */
+        ++a;  /* round - this step may add a significant bit */
+        a >>= 2;  /* dump Q and R */
+        /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
+        if (a & ((tu_int)1 << DBL_MANT_DIG))
+        {
+            a >>= 1;
+            ++e;
+        }
+        /* a is now rounded to DBL_MANT_DIG bits */
+    }
+    else
+    {
+        a <<= (DBL_MANT_DIG - sd);
+        /* a is now rounded to DBL_MANT_DIG bits */
+    }
+    double_bits fb;
+    fb.u.s.high = ((su_int)s & 0x80000000) |        /* sign */
+                ((e + 1023) << 20)      |        /* exponent */
+                ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
+    fb.u.s.low = (su_int)a;                         /* mantissa-low */
+    return fb.f;
+}
+
+#endif