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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1186 | savelij | 1 | /* aplfloat.c */ |
| 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 | /* APPLE<->IEEE Floating Point Conversion on host */ |
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| 8 | /* */ |
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| 9 | /*****************************************************************************/ |
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| 10 | |||
| 11 | #include "stdinc.h" |
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| 12 | #include <errno.h> |
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| 13 | #include <string.h> |
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| 14 | |||
| 15 | #include "errmsg.h" |
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| 16 | #include "asmerr.h" |
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| 17 | #include "strcomp.h" |
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| 18 | #include "as_float.h" |
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| 19 | #include "aplfloat.h" |
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| 20 | |||
| 21 | /*!------------------------------------------------------------------------ |
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| 22 | * \fn as_float_2_apl4(as_float_t inp, Word *p_dest) |
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| 23 | * \brief convert from host to Apple II 4 byte float format |
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| 24 | * \param inp value to dispose |
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| 25 | * \param p_dest where to dispose |
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| 26 | * \return 0 or error code (<0) |
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| 27 | * ------------------------------------------------------------------------ */ |
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| 28 | |||
| 29 | int as_float_2_apl4(as_float_t inp, Word *p_dest) |
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| 30 | { |
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| 31 | Boolean round_up; |
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| 32 | as_float_dissect_t dissect; |
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| 33 | |||
| 34 | /* Dissect number: */ |
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| 35 | |||
| 36 | as_float_dissect(&dissect, inp); |
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| 37 | |||
| 38 | /* NaN and Infinity cannot be represented: */ |
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| 39 | |||
| 40 | if ((dissect.fp_class == AS_FP_NAN) |
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| 41 | || (dissect.fp_class == AS_FP_INFINITE)) |
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| 42 | return -EINVAL; |
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| 43 | |||
| 44 | /* (3) Denormalize small numbers: */ |
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| 45 | |||
| 46 | while ((dissect.exponent < -128) && !as_float_mantissa_is_zero(&dissect)) |
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| 47 | { |
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| 48 | dissect.exponent++; |
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| 49 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 50 | } |
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| 51 | |||
| 52 | /* Build Two's complement. Note the sign becomes part of the |
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| 53 | mantissa, which is afterwards one bit longer: */ |
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| 54 | |||
| 55 | as_float_mantissa_twos_complement(&dissect); |
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| 56 | |||
| 57 | /* Normalize, so that topmost bits of mantissa are unequal. This happens |
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| 58 | for powers of two, after negating: */ |
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| 59 | |||
| 60 | switch (as_float_mantissa_extract(&dissect, 0, 2)) |
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| 61 | { |
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| 62 | case 0: |
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| 63 | case 3: |
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| 64 | if (dissect.exponent > -128) |
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| 65 | { |
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| 66 | dissect.exponent--; |
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| 67 | as_float_mantissa_shift_left(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 68 | } |
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| 69 | break; |
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| 70 | } |
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| 71 | |||
| 72 | /* (4) Round mantissa. We will use 24 of them. So the "half LSB" bit |
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| 73 | to look at is bit 24, seen from left: */ |
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| 74 | |||
| 75 | if (as_float_get_mantissa_bit(dissect.mantissa, dissect.mantissa_bits, 24)) |
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| 76 | { |
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| 77 | if (!as_float_mantissa_is_zero_from(&dissect, 25)) /* > 0.5 */ |
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| 78 | round_up = True; |
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| 79 | else /* == 0.5 */ |
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| 80 | round_up = as_float_get_mantissa_bit(dissect.mantissa, dissect.mantissa_bits, 23); |
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| 81 | } |
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| 82 | else /* < 0.5 */ |
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| 83 | round_up = False; |
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| 84 | |||
| 85 | if (round_up) |
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| 86 | { |
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| 87 | as_float_mant_t round_sum; |
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| 88 | |||
| 89 | (void)as_float_mantissa_add_bit(round_sum, dissect.mantissa, 24, dissect.mantissa_bits); |
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| 90 | |||
| 91 | /* overflow during round-up? */ |
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| 92 | |||
| 93 | if ((round_sum[0] ^ dissect.mantissa[0]) & 0x80000000ul) |
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| 94 | { |
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| 95 | dissect.exponent++; |
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| 96 | /* Arithmetic right shift of signed number to preserve sign: */ |
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| 97 | as_float_mantissa_shift_right(round_sum, as_float_get_mantissa_bit(dissect.mantissa, dissect.mantissa_bits, 0), dissect.mantissa_bits); |
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| 98 | } |
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| 99 | |||
| 100 | memcpy(dissect.mantissa, round_sum, sizeof(dissect.mantissa)); |
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| 101 | } |
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| 102 | |||
| 103 | /* After knowing final exponent, check for overflow: */ |
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| 104 | |||
| 105 | if (dissect.exponent > 127) |
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| 106 | return -E2BIG; |
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| 107 | |||
| 108 | /* (5) mantissa zero means exponent is also zero */ |
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| 109 | |||
| 110 | if (as_float_mantissa_is_zero(&dissect)) |
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| 111 | dissect.exponent = 0; |
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| 112 | |||
| 113 | /* (7) Assemble: */ |
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| 114 | |||
| 115 | p_dest[0] = (((dissect.exponent + 128) << 8) & 0xff00ul) |
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| 116 | | as_float_mantissa_extract(&dissect, 0, 8); |
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| 117 | p_dest[1] = as_float_mantissa_extract(&dissect, 8, 16); |
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| 118 | |||
| 119 | return 0; |
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| 120 | } |