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Diffstat (limited to 'lib/floatuntixf.c')
-rw-r--r-- | lib/floatuntixf.c | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/lib/floatuntixf.c b/lib/floatuntixf.c new file mode 100644 index 000000000..a28db10f6 --- /dev/null +++ b/lib/floatuntixf.c @@ -0,0 +1,80 @@ +//===-- floatuntixf.c - Implement __floatuntixf ---------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements __floatuntixf 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 +// 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 + +si_int __clzti2(ti_int a); + +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.low = (e + 16383); // exponent + fb.u.low.all = (du_int)a; // mantissa + return fb.f; +} + +#endif |