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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1186 | savelij | 1 | /* milfloat.h */ |
| 2 | /*****************************************************************************/ |
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| 3 | /* SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only */ |
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| 4 | /* */ |
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| 5 | /* AS */ |
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| 6 | /* */ |
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| 7 | /* IEEE -> MIL STD 1750 Floating Point Conversion on host */ |
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| 8 | /* */ |
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| 9 | /*****************************************************************************/ |
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| 10 | |||
| 11 | #include <stdio.h> |
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| 12 | #include <errno.h> |
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| 13 | #include "as_float.h" |
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| 14 | #include "milfloat.h" |
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| 15 | |||
| 16 | /*!------------------------------------------------------------------------ |
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| 17 | * \fn as_float_2_mil1750(as_float_t inp, Word *p_dest, Boolean extended) |
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| 18 | * \brief convert host float to MIL STD 1750 |
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| 19 | * \param inp number to convert |
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| 20 | * \param p_dest destination buffer |
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| 21 | * \param extended convert to 32 or 48 bit format? |
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| 22 | * \return # of words written or < 0 if error |
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| 23 | * ------------------------------------------------------------------------ */ |
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| 24 | |||
| 25 | int as_float_2_mil1750(as_float_t inp, Word *p_dest, Boolean extended) |
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| 26 | { |
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| 27 | as_float_dissect_t dissect; |
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| 28 | Word or_sum; |
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| 29 | unsigned req_mantissa_bits; |
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| 30 | |||
| 31 | /* Dissect number: */ |
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| 32 | |||
| 33 | as_float_dissect(&dissect, inp); |
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| 34 | |||
| 35 | /* NaN and Infinity cannot be represented: */ |
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| 36 | |||
| 37 | if ((dissect.fp_class == AS_FP_NAN) |
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| 38 | || (dissect.fp_class == AS_FP_INFINITE)) |
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| 39 | return -EINVAL; |
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| 40 | |||
| 41 | /* Mantissa is in range [-1,+1) instead of [-2,+2): */ |
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| 42 | |||
| 43 | dissect.exponent++; |
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| 44 | |||
| 45 | /* If exponent is too small to represent, shift down mantissa |
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| 46 | until exponent is large enough, or mantissa is all-zeroes: */ |
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| 47 | |||
| 48 | while ((dissect.exponent < -128) && !as_float_mantissa_is_zero(&dissect)) |
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| 49 | { |
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| 50 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 51 | dissect.exponent++; |
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| 52 | } |
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| 53 | |||
| 54 | /* exponent overflow? */ |
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| 55 | |||
| 56 | if (dissect.exponent > 127) |
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| 57 | return -E2BIG; |
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| 58 | |||
| 59 | /* Form 2s complement of mantissa when sign is set: */ |
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| 60 | |||
| 61 | as_float_mantissa_twos_complement(&dissect); |
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| 62 | |||
| 63 | /* Normalize, so that topmost bits of mantissa are unequal. This happens |
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| 64 | for powers of two, after negating: */ |
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| 65 | |||
| 66 | switch (as_float_mantissa_extract(&dissect, 0, 2)) |
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| 67 | { |
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| 68 | case 0: |
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| 69 | case 3: |
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| 70 | if (dissect.exponent > -127) /* -128? */ |
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| 71 | { |
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| 72 | dissect.exponent--; |
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| 73 | as_float_mantissa_shift_left(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 74 | } |
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| 75 | break; |
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| 76 | } |
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| 77 | |||
| 78 | /* no rounding: */ |
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| 79 | |||
| 80 | req_mantissa_bits = extended ? 40 : 24; |
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| 81 | if (req_mantissa_bits > dissect.mantissa_bits) |
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| 82 | as_float_append_mantissa_bits(&dissect, 0, req_mantissa_bits - dissect.mantissa_bits); |
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| 83 | |||
| 84 | /* Write out result: */ |
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| 85 | |||
| 86 | or_sum = (p_dest[0] = as_float_mantissa_extract(&dissect, 0, 16)); |
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| 87 | or_sum |= (p_dest[1] = as_float_mantissa_extract(&dissect, 16, 8) << 8); |
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| 88 | if (extended) |
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| 89 | or_sum |= (p_dest[2] = as_float_mantissa_extract(&dissect, 24, 16)); |
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| 90 | |||
| 91 | /* zero mantissa means zero exponent */ |
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| 92 | |||
| 93 | if (or_sum) |
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| 94 | p_dest[1] |= dissect.exponent & 0xff; |
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| 95 | |||
| 96 | return extended ? 3 : 2; |
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| 97 | } |