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Diffstat (limited to 'lib/builtins/floatdidf.c')
| -rw-r--r-- | lib/builtins/floatdidf.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/lib/builtins/floatdidf.c b/lib/builtins/floatdidf.c new file mode 100644 index 000000000000..e53fa2580f6e --- /dev/null +++ b/lib/builtins/floatdidf.c @@ -0,0 +1,107 @@ +/*===-- floatdidf.c - Implement __floatdidf -------------------------------=== + * + * 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 __floatdidf for the compiler_rt library. + * + *===----------------------------------------------------------------------=== + */ + +#include "int_lib.h" + +/* Returns: convert a to a double, rounding toward even. */ + +/* Assumption: double is a IEEE 64 bit floating point type + * di_int is a 64 bit integral type + */ + +/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ + +ARM_EABI_FNALIAS(l2d, floatdidf) + +#ifndef __SOFT_FP__ +/* Support for systems that have hardware floating-point; we'll set the inexact flag + * as a side-effect of this computation. + */ + +COMPILER_RT_ABI double +__floatdidf(di_int a) +{ + static const double twop52 = 0x1.0p52; + static const double twop32 = 0x1.0p32; + + union { int64_t x; double d; } low = { .d = twop52 }; + + const double high = (int32_t)(a >> 32) * twop32; + low.x |= a & INT64_C(0x00000000ffffffff); + + const double result = (high - twop52) + low.d; + return result; +} + +#else +/* Support for systems that don't have hardware floating-point; there are no flags to + * set, and we don't want to code-gen to an unknown soft-float implementation. + */ + +COMPILER_RT_ABI double +__floatdidf(di_int a) +{ + if (a == 0) + return 0.0; + const unsigned N = sizeof(di_int) * CHAR_BIT; + const di_int s = a >> (N-1); + a = (a ^ s) - s; + int sd = N - __builtin_clzll(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 = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) | + ((a & ((du_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 & ((du_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.high = ((su_int)s & 0x80000000) | /* sign */ + ((e + 1023) << 20) | /* exponent */ + ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ + fb.u.low = (su_int)a; /* mantissa-low */ + return fb.f; +} +#endif |