[builtins] Implement __floattitf() & __floatuntitf()

Implement the missing __floattitf() and __floatuntitf() functions, to
convert 128-bit (unsigned) integers to quad-precision floating-point
types. This is needed e.g. on AArch64 where 'long double' is
a quad-precision type.

The code is based on the existing code for __floattixf()
and __floatuntixf(), updated to account for different bit field lengths
of quad-precision float. The tests are also copied, with the rounding
tests adjusted for longer significand.

Differential Revision: https://reviews.llvm.org/D27898

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@291259 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 79 insertions, 0 deletions

diff --git a/lib/builtins/floatuntitf.c b/lib/builtins/floatuntitf.c
new file mode 100644
index 000000000..e2518c93f
--- /dev/null
+++ b/lib/builtins/floatuntitf.c
@@ -0,0 +1,79 @@
+//===-- lib/floatuntitf.c - uint128 -> quad-precision conversion --*- C -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements tu_int to quad-precision conversion for the
+// compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
+// mode.
+//
+//===----------------------------------------------------------------------===//
+
+#define QUAD_PRECISION
+#include "fp_lib.h"
+#include "int_lib.h"
+
+/* Returns: convert a tu_int to a fp_t, rounding toward even. */
+
+/* Assumption: fp_t is a IEEE 128 bit floating point type
+ *             tu_int is a 128 bit integral type
+ */
+
+/* seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm |
+ * mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
+ */
+
+#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+COMPILER_RT_ABI fp_t
+__floatuntitf(tu_int a) {
+    if (a == 0)
+        return 0.0;
+    const unsigned N = sizeof(tu_int) * CHAR_BIT;
+    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 = (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.all = (du_int)(e + 16383) << 48            /* exponent */
+                  | ((a >> 64) & 0x0000ffffffffffffLL);  /* significand */
+    fb.u.low.all = (du_int)(a);
+    return fb.f;
+}
+
+#endif