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228 lines
5.5 KiB
C
228 lines
5.5 KiB
C
/* Half-float conversion routines.
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Copyright (C) 2008-2019 Free Software Foundation, Inc.
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Contributed by CodeSourcery.
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This file is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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This file is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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struct format
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{
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/* Number of bits. */
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unsigned long long size;
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/* Exponent bias. */
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unsigned long long bias;
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/* Exponent width in bits. */
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unsigned long long exponent;
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/* Significand precision in explicitly stored bits. */
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unsigned long long significand;
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};
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static const struct format
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binary32 =
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{
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32, /* size. */
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127, /* bias. */
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8, /* exponent. */
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23 /* significand. */
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};
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static const struct format
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binary64 =
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{
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64, /* size. */
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1023, /* bias. */
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11, /* exponent. */
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52 /* significand. */
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};
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static inline unsigned short
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__gnu_float2h_internal (const struct format* fmt,
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unsigned long long a, int ieee)
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{
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unsigned long long point = 1ULL << fmt->significand;
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unsigned short sign = (a >> (fmt->size - 16)) & 0x8000;
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int aexp;
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unsigned long long mantissa;
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unsigned long long mask;
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unsigned long long increment;
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/* Get the exponent and mantissa encodings. */
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mantissa = a & (point - 1);
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mask = (1 << fmt->exponent) - 1;
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aexp = (a >> fmt->significand) & mask;
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/* Infinity, NaN and alternative format special case. */
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if (((unsigned int) aexp) == mask)
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{
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if (!ieee)
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return sign;
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if (mantissa == 0)
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return sign | 0x7c00; /* Infinity. */
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/* Remaining cases are NaNs. Convert SNaN to QNaN. */
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return sign | 0x7e00 | (mantissa >> (fmt->significand - 10));
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}
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/* Zero. */
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if (aexp == 0 && mantissa == 0)
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return sign;
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/* Construct the exponent and mantissa. */
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aexp -= fmt->bias;
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/* Decimal point is immediately after the significand. */
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mantissa |= point;
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if (aexp < -14)
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{
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mask = point | (point - 1);
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/* Minimum exponent for half-precision is 2^-24. */
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if (aexp >= -25)
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mask >>= 25 + aexp;
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}
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else
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mask = (point - 1) >> 10;
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/* Round. */
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if (mantissa & mask)
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{
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increment = (mask + 1) >> 1;
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if ((mantissa & mask) == increment)
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increment = mantissa & (increment << 1);
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mantissa += increment;
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if (mantissa >= (point << 1))
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{
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mantissa >>= 1;
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aexp++;
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}
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}
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if (ieee)
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{
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if (aexp > 15)
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return sign | 0x7c00;
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}
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else
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{
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if (aexp > 16)
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return sign | 0x7fff;
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}
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if (aexp < -24)
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return sign;
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if (aexp < -14)
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{
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mantissa >>= -14 - aexp;
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aexp = -14;
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}
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/* Encode the final 16-bit floating-point value.
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This is formed of the sign bit, the bias-adjusted exponent, and the
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calculated mantissa, with the following caveats:
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1. The mantissa calculated after rounding could have a leading 1.
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To compensate for this, subtract one from the exponent bias (15)
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before adding it to the calculated exponent.
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2. When we were calculating rounding, we left the mantissa with the
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number of bits of the source operand, it needs reduced to ten
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bits (+1 for the afforementioned leading 1) by shifting right by
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the number of bits in the source mantissa - 10.
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3. To ensure the leading 1 in the mantissa is applied to the exponent
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we need to add the mantissa rather than apply an arithmetic "or"
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to it. */
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return sign | (((aexp + 14) << 10) + (mantissa >> (fmt->significand - 10)));
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}
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static inline unsigned short
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__gnu_f2h_internal (unsigned int a, int ieee)
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{
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return __gnu_float2h_internal (&binary32, (unsigned long long) a, ieee);
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}
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static inline unsigned short
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__gnu_d2h_internal (unsigned long long a, int ieee)
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{
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return __gnu_float2h_internal (&binary64, a, ieee);
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}
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unsigned int
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__gnu_h2f_internal(unsigned short a, int ieee)
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{
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unsigned int sign = (unsigned int)(a & 0x8000) << 16;
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int aexp = (a >> 10) & 0x1f;
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unsigned int mantissa = a & 0x3ff;
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if (aexp == 0x1f && ieee)
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return sign | 0x7f800000 | (mantissa << 13);
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if (aexp == 0)
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{
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int shift;
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if (mantissa == 0)
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return sign;
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shift = __builtin_clz(mantissa) - 21;
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mantissa <<= shift;
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aexp = -shift;
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}
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return sign | (((aexp + 0x70) << 23) + (mantissa << 13));
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}
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unsigned short
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__gnu_f2h_ieee(unsigned int a)
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{
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return __gnu_f2h_internal(a, 1);
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}
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unsigned int
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__gnu_h2f_ieee(unsigned short a)
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{
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return __gnu_h2f_internal(a, 1);
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}
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unsigned short
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__gnu_f2h_alternative(unsigned int x)
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{
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return __gnu_f2h_internal(x, 0);
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}
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unsigned int
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__gnu_h2f_alternative(unsigned short a)
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{
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return __gnu_h2f_internal(a, 0);
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}
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unsigned short
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__gnu_d2h_ieee (unsigned long long a)
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{
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return __gnu_d2h_internal (a, 1);
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}
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unsigned short
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__gnu_d2h_alternative (unsigned long long x)
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{
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return __gnu_d2h_internal (x, 0);
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}
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