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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1186 | savelij | 1 | /* ibmfloat.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-Portierung */ |
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| 6 | /* */ |
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| 7 | /* IBM Floating Point Format */ |
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| 8 | /* */ |
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| 9 | /*****************************************************************************/ |
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| 10 | |||
| 11 | /***************************************************************************** |
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| 12 | * Includes |
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| 13 | *****************************************************************************/ |
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| 14 | |||
| 15 | #include "stdinc.h" |
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| 16 | #include <math.h> |
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| 17 | #include <string.h> |
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| 18 | |||
| 19 | #include "as_float.h" |
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| 20 | #include "errmsg.h" |
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| 21 | #include "asmerr.h" |
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| 22 | #include "ibmfloat.h" |
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| 23 | |||
| 24 | /*!------------------------------------------------------------------------ |
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| 25 | * \fn as_float_2_ibm_float(Word *pDest, as_float_t Src, Boolean ToDouble) |
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| 26 | * \brief convert floating point number to IBM single precision format |
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| 27 | * \param pDest where to write result (2 words) |
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| 28 | * \param Src floating point number to store |
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| 29 | * \param ToDouble convert to double precision (64 instead of 32 bits)? |
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| 30 | * \return 0 or error code |
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| 31 | * ------------------------------------------------------------------------ */ |
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| 32 | |||
| 33 | int as_float_2_ibm_float(Word *pDest, as_float_t Src, Boolean ToDouble) |
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| 34 | { |
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| 35 | as_float_dissect_t dissect; |
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| 36 | unsigned dest_num_bits; |
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| 37 | |||
| 38 | /* (1) Dissect IEEE number */ |
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| 39 | |||
| 40 | as_float_dissect(&dissect, Src); |
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| 41 | |||
| 42 | /* NaN or infinity not representable: */ |
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| 43 | |||
| 44 | if ((dissect.fp_class != AS_FP_NORMAL) |
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| 45 | && (dissect.fp_class != AS_FP_SUBNORMAL)) |
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| 46 | return -EINVAL; |
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| 47 | |||
| 48 | /* IBM format mantissa is in range [0.5,1) instead of [1,2): */ |
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| 49 | |||
| 50 | dissect.exponent++; |
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| 51 | |||
| 52 | /* (2) Convert 2^n exponent to multiple of four since IBM float exponent is to the base of 16. |
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| 53 | Note that before shifting, we ad a zero bit at the end to avoid losing precision: */ |
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| 54 | |||
| 55 | while (dissect.exponent & 3) |
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| 56 | { |
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| 57 | as_float_append_mantissa_bits(&dissect, 0, 1); |
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| 58 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 59 | dissect.exponent++; |
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| 60 | } |
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| 61 | |||
| 62 | /* (3) make base-16 exponent explicit */ |
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| 63 | |||
| 64 | dissect.exponent /= 4; |
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| 65 | |||
| 66 | /* (4) Round to target precision. We cannot use as_float_round() for rounding |
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| 67 | since the exponent is already base-16: */ |
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| 68 | |||
| 69 | dest_num_bits = ToDouble ? 56 : 24; |
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| 70 | if (dest_num_bits > dissect.mantissa_bits) |
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| 71 | as_float_round(&dissect, dest_num_bits); |
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| 72 | else if (dest_num_bits < dissect.mantissa_bits) |
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| 73 | { |
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| 74 | Boolean round_up; |
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| 75 | |||
| 76 | if (as_float_get_mantissa_bit(dissect.mantissa, dissect.mantissa_bits, dest_num_bits)) |
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| 77 | { |
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| 78 | if (!as_float_mantissa_is_zero_from(&dissect, dest_num_bits + 1)) /* > 0.5 */ |
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| 79 | round_up = True; |
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| 80 | else |
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| 81 | round_up = !!as_float_get_mantissa_bit(dissect.mantissa, dissect.mantissa_bits, dest_num_bits - 1); |
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| 82 | } |
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| 83 | else /* < 0.5 */ |
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| 84 | round_up = False; |
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| 85 | |||
| 86 | if (round_up) |
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| 87 | { |
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| 88 | as_float_mant_word_t carry; |
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| 89 | as_float_mant_t sum; |
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| 90 | |||
| 91 | carry = as_float_mantissa_add_bit(sum, dissect.mantissa, dest_num_bits, dissect.mantissa_bits); |
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| 92 | if (carry) |
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| 93 | { |
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| 94 | as_float_mantissa_shift_right(sum, carry, dissect.mantissa_bits); |
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| 95 | as_float_mantissa_shift_right(sum, 0, dissect.mantissa_bits); |
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| 96 | as_float_mantissa_shift_right(sum, 0, dissect.mantissa_bits); |
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| 97 | as_float_mantissa_shift_right(sum, 0, dissect.mantissa_bits); |
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| 98 | dissect.exponent++; |
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| 99 | } |
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| 100 | memcpy(dissect.mantissa, sum, sizeof dissect.mantissa); |
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| 101 | } |
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| 102 | as_float_remove_mantissa_bits(&dissect, dissect.mantissa_bits - dest_num_bits); |
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| 103 | } |
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| 104 | |||
| 105 | /* Overrange? */ |
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| 106 | |||
| 107 | if (dissect.exponent > 63) |
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| 108 | return -E2BIG; |
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| 109 | |||
| 110 | /* number that is too small may degenerate to 0: */ |
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| 111 | |||
| 112 | while ((dissect.exponent < -64) && !as_float_mantissa_is_zero(&dissect)) |
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| 113 | { |
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| 114 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 115 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 116 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 117 | as_float_mantissa_shift_right(dissect.mantissa, 0, dissect.mantissa_bits); |
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| 118 | dissect.exponent++; |
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| 119 | } |
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| 120 | |||
| 121 | /* Zero shall get zero (-64) as exponent: */ |
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| 122 | |||
| 123 | if (as_float_mantissa_is_zero(&dissect)) |
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| 124 | dissect.exponent = -64; |
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| 125 | |||
| 126 | if (dissect.exponent < -64) |
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| 127 | dissect.exponent = -64; |
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| 128 | |||
| 129 | /* add bias to exponent */ |
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| 130 | |||
| 131 | dissect.exponent += 64; |
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| 132 | |||
| 133 | /* store result: */ |
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| 134 | |||
| 135 | pDest[0] = (dissect.negative << 15) |
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| 136 | | ((dissect.exponent << 8) & 0x7f00) |
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| 137 | | as_float_mantissa_extract(&dissect, 0, 8); |
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| 138 | pDest[1] = as_float_mantissa_extract(&dissect, 8, 16); |
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| 139 | if (ToDouble) |
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| 140 | { |
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| 141 | pDest[2] = as_float_mantissa_extract(&dissect, 24, 16); |
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| 142 | pDest[3] = as_float_mantissa_extract(&dissect, 40, 16); |
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| 143 | } |
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| 144 | |||
| 145 | return 0; |
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| 146 | } |