Initial import

third_party/compiler_rt/floatuntixf.c

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+/* clang-format off */
+/* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------===
+ *
+ *                     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 __floatuntixf for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+STATIC_YOINK("huge_compiler_rt_license");
+
+#include "third_party/compiler_rt/int_lib.h"
+
+#ifdef CRT_HAS_128BIT
+
+/* 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
+ *             tu_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
+ */
+
+COMPILER_RT_ABI long double
+__floatuntixf(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.s.low = (e + 16383);                  /* exponent */
+    fb.u.low.all = (du_int)a;                     /* mantissa */
+    return fb.f;
+}
+
+#endif