From b3a6901e66f55b35aa9e01bcb24134e6a65ea004 Mon Sep 17 00:00:00 2001
From: Daniel Dunbar <daniel@zuster.org>
Date: Fri, 26 Jun 2009 16:47:03 +0000
Subject: Initial import of compiler-rt.  -

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@74292 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/floattixf.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 lib/floattixf.c

(limited to 'lib/floattixf.c')

diff --git a/lib/floattixf.c b/lib/floattixf.c
new file mode 100644
index 00000000..520b6ed0
--- /dev/null
+++ b/lib/floattixf.c
@@ -0,0 +1,83 @@
+//===-- floattixf.c - Implement __floattixf -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __floattixf for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#if __x86_64
+
+#include "int_lib.h"
+#include <float.h>
+
+// Returns: convert a to a long double, rounding toward even.
+
+// Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
+//             ti_int is a 128 bit integral type
+
+// gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
+// 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
+
+si_int __clzti2(ti_int a);
+
+long double
+__floattixf(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 > LDBL_MANT_DIG)
+    {
+        //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
+        //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
+        //                                                12345678901234567890123456
+        //  1 = msb 1 bit
+        //  P = bit LDBL_MANT_DIG-1 bits to the right of 1
+        //  Q = bit LDBL_MANT_DIG bits to the right of 1
+        //  R = "or" of all bits to the right of Q
+        switch (sd)
+        {
+        case LDBL_MANT_DIG + 1:
+            a <<= 1;
+            break;
+        case LDBL_MANT_DIG + 2:
+            break;
+        default:
+            a = ((tu_int)a >> (sd - (LDBL_MANT_DIG+2))) |
+                ((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
+        if (a & ((tu_int)1 << LDBL_MANT_DIG))
+        {
+            a >>= 1;
+            ++e;
+        }
+        // a is now rounded to LDBL_MANT_DIG bits
+    }
+    else
+    {
+        a <<= (LDBL_MANT_DIG - sd);
+        // a is now rounded to LDBL_MANT_DIG bits
+    }
+    long_double_bits fb;
+    fb.u.high.low = ((su_int)s & 0x8000) |        // sign
+                    (e + 16383);                  // exponent
+    fb.u.low.all = (du_int)a;                     // mantissa
+    return fb.f;
+}
+
+#endif
-- 
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