libgcc/soft-fp/fixddbitint.c

   1 /* Software floating-point emulation.
   2    Convert _Decimal64 to signed or unsigned _BitInt.
   3
   4    Copyright (C) 2023 Free Software Foundation, Inc.
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 Under Section 7 of GPL version 3, you are granted additional
  19 permissions described in the GCC Runtime Library Exception, version
  20 3.1, as published by the Free Software Foundation.
  21
  22 You should have received a copy of the GNU General Public License and
  23 a copy of the GCC Runtime Library Exception along with this program;
  24 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  25 <http://www.gnu.org/licenses/>.  */
  26
  27 #include "soft-fp.h"
  28 #include "bitint.h"
  29
  30 #ifdef __BITINT_MAXWIDTH__
  31 extern void __bid_fixddbitint (UBILtype *, SItype, _Decimal64);
  32
  33 void
  34 __bid_fixddbitint (UBILtype *r, SItype rprec, _Decimal64 a)
  35 {
  36   FP_DECL_EX;
  37   USItype arprec = rprec < 0 ? -rprec : rprec;
  38   USItype rn = (arprec + BIL_TYPE_SIZE - 1) / BIL_TYPE_SIZE;
  39   union { _Decimal64 d; UDItype u; } u;
  40   UDItype mantissa, t;
  41   SItype sgn;
  42   SItype exponent;
  43   USItype exp_bits, mant_bits;
  44   UBILtype *pow10v, *resv;
  45   USItype pow10_limbs, res_limbs, min_limbs, mant_limbs, low_zeros;
  46
  47   FP_INIT_EXCEPTIONS;
  48   u.d = a;
  49   t = u.u >> 51;
  50   sgn = (DItype) u.u < 0;
  51   if ((t & (3 << 10)) != (3 << 10))
  52     {
  53       mantissa = u.u & ((((UDItype) 1) << 53) - 1);
  54       exponent = (t >> 2) & 0x3ff;
  55     }
  56   else if ((t & (3 << 8)) != (3 << 8))
  57     {
  58       mantissa = u.u & ((((UDItype) 1) << 51) - 1);
  59       mantissa |= ((UDItype) 1) << 53;
  60       exponent = t & 0x3ff;
  61       if (mantissa > (UDItype) 9999999999999999)
  62         mantissa = 0;
  63     }
  64   else
  65     {
  66       FP_SET_EXCEPTION (FP_EX_INVALID
  67                         | FP_EX_INVALID_CVI
  68                         | ((FP_EX_INVALID_SNAN
  69                             && ((t & 0x80)) != 0)
  70                            ? FP_EX_INVALID_SNAN : 0));
  71     ovf:
  72       if (!sgn)
  73         __builtin_memset (r, -1, rn * sizeof (UBILtype));
  74       else
  75         __builtin_memset (r, 0, rn * sizeof (UBILtype));
  76       if (sgn ^ (rprec >= 0))
  77         r[BITINT_END (0, rn - 1)]
  78           |= (UBILtype) -1 << ((arprec - 1) % BIL_TYPE_SIZE);
  79       else
  80         r[BITINT_END (0, rn - 1)]
  81           &= ~((UBILtype) -1 << ((arprec - 1) % BIL_TYPE_SIZE));
  82       goto done;
  83     }
  84   exponent -= 398;
  85
  86   if (mantissa == 0)
  87     {
  88       /* Zero (with any exponent).  */
  89     zero:
  90       __builtin_memset (r, 0, rn * sizeof (UBILtype));
  91       goto done;
  92     }
  93   if (exponent <= -16)
  94     {
  95       FP_SET_EXCEPTION (FP_EX_INEXACT);
  96       goto zero;
  97     }
  98   else if (exponent < 0)
  99     {
 100       UBILtype limbs[64 / BIL_TYPE_SIZE];
 101       UDItype d, rem;
 102       __bid_pow10bitint (limbs, 64, -exponent);
 103 #if BIL_TYPE_SIZE == 64
 104       d = limbs[0];
 105 #elif BIL_TYPE_SIZE == 32
 106       d = (UDItype) limbs[BITINT_END (0, 1)] << 32 | limbs[BITINT_END (1, 0)];
 107 #else
 108 # error Unsupported BIL_TYPE_SIZE
 109 #endif
 110       rem = mantissa % d;
 111       mantissa /= d;
 112       if (rem)
 113         FP_SET_EXCEPTION (FP_EX_INEXACT);
 114       if (mantissa == 0)
 115         goto zero;
 116       exponent = 0;
 117     }
 118
 119   if (rprec >= 0 && sgn)
 120     {
 121     ovf_ex:
 122       FP_SET_EXCEPTION (FP_EX_INVALID | FP_EX_INVALID_CVI);
 123       goto ovf;
 124     }
 125
 126   /* Lower estimate for number of bits needed for pow10 (exponent).  */
 127   exp_bits = exponent / 3;
 128   exp_bits = exp_bits * 10 - exp_bits / 29;
 129   mant_bits = sizeof (0ULL) * __CHAR_BIT__ - __builtin_clzll (mantissa);
 130   if (exp_bits + mant_bits > arprec + 1)
 131     goto ovf_ex;
 132   /* Upper estimate for number of bits needed for pow10 (exponent).  */
 133   exp_bits = (exponent + 2) / 3;
 134   exp_bits = exp_bits * 10 - exp_bits / 30;
 135   if (exp_bits == 0)
 136     exp_bits = 1;
 137   pow10_limbs = (exp_bits + BIL_TYPE_SIZE - 1) / BIL_TYPE_SIZE;
 138   pow10v = __builtin_alloca (pow10_limbs * sizeof (UBILtype));
 139   low_zeros = __bid_pow10bitint (pow10v, exp_bits, exponent);
 140
 141   res_limbs = ((exp_bits + mant_bits + BIL_TYPE_SIZE - 1)
 142                / BIL_TYPE_SIZE) - low_zeros;
 143   mant_limbs = (mant_bits + BIL_TYPE_SIZE - 1) / BIL_TYPE_SIZE;
 144   resv = __builtin_alloca ((res_limbs + mant_limbs) * sizeof (UBILtype));
 145 #if BIL_TYPE_SIZE >= 64
 146   resv[res_limbs] = mantissa;
 147 #else
 148   if (mant_limbs == 1)
 149     resv[res_limbs] = mantissa;
 150   else
 151     {
 152       resv[res_limbs + BITINT_END (1, 0)] = mantissa;
 153       resv[res_limbs + BITINT_END (0, 1)] = mantissa >> 32;
 154     }
 155 #endif
 156   __mulbitint3 (resv, exp_bits + mant_bits - low_zeros * BIL_TYPE_SIZE,
 157                 resv + res_limbs, mant_bits,
 158                 pow10v + BITINT_END (0, low_zeros),
 159                 exp_bits - low_zeros * BIL_TYPE_SIZE);
 160   if (res_limbs + low_zeros >= rn)
 161     {
 162       if (res_limbs + low_zeros > rn && resv[BITINT_END (0, res_limbs - 1)])
 163         goto ovf_ex;
 164       if ((arprec % BIL_TYPE_SIZE) != 0
 165           && (resv[BITINT_END (rn - res_limbs, rn - 1) - low_zeros]
 166               & ((UBILtype) -1 << (arprec % BIL_TYPE_SIZE))) != 0)
 167         goto ovf_ex;
 168       min_limbs = rn - low_zeros;
 169     }
 170   else
 171     min_limbs = res_limbs;
 172   if (low_zeros)
 173     __builtin_memset (r + BITINT_END (rn - low_zeros, 0), '\0',
 174                       low_zeros * sizeof (UBILtype));
 175   if (sgn)
 176     bitint_negate (r + BITINT_END (rn - low_zeros - 1, low_zeros),
 177                    resv + BITINT_END (res_limbs - 1, 0), min_limbs);
 178   else
 179     __builtin_memcpy (r + BITINT_END (rn - low_zeros - min_limbs, low_zeros),
 180                       resv + BITINT_END (res_limbs - min_limbs, 0),
 181                       min_limbs * sizeof (UBILtype));
 182   if (res_limbs + low_zeros < rn)
 183     {
 184       if (sgn)
 185         __builtin_memset (r + BITINT_END (0, res_limbs + low_zeros), -1,
 186                           (rn - res_limbs - low_zeros) * sizeof (UBILtype));
 187       else
 188         __builtin_memset (r + BITINT_END (0, res_limbs + low_zeros), '\0',
 189                           (rn - res_limbs - low_zeros) * sizeof (UBILtype));
 190     }
 191   else if (sgn)
 192     {
 193       if ((r[BITINT_END (0, rn - 1)]
 194            & ((UBILtype) 1 << ((arprec - 1) % BIL_TYPE_SIZE))) == 0)
 195         goto ovf_ex;
 196     }
 197   else if (rprec < 0
 198            && (r[BITINT_END (0, rn - 1)]
 199                & ((UBILtype) 1 << ((arprec - 1) % BIL_TYPE_SIZE))) != 0)
 200     goto ovf_ex;
 201
 202 done:
 203   FP_HANDLE_EXCEPTIONS;
 204 }
 205 #endif