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| 731 | cejka | 1 | /* |
| 2 | * Copyright (C) 2005 Josef Cejka |
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| 3 | * All rights reserved. |
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| 4 | * |
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| 5 | * Redistribution and use in source and binary forms, with or without |
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| 6 | * modification, are permitted provided that the following conditions |
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| 7 | * are met: |
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| 8 | * |
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| 9 | * - Redistributions of source code must retain the above copyright |
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| 10 | * notice, this list of conditions and the following disclaimer. |
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| 11 | * - Redistributions in binary form must reproduce the above copyright |
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| 12 | * notice, this list of conditions and the following disclaimer in the |
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| 13 | * documentation and/or other materials provided with the distribution. |
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| 14 | * - The name of the author may not be used to endorse or promote products |
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| 15 | * derived from this software without specific prior written permission. |
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| 16 | * |
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| 17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
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| 18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
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| 19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
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| 20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
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| 21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
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| 22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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| 23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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| 24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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| 25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
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| 26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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| 27 | */ |
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| 28 | |||
| 29 | #include "sftypes.h" |
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| 30 | #include "sub.h" |
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| 31 | |||
| 32 | /** Subtract two float32 numbers with same signs |
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| 33 | */ |
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| 34 | float32 subFloat32(float32 a, float32 b) |
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| 35 | { |
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| 36 | int expdiff; |
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| 37 | __u32 exp1,exp2,mant1,mant2; |
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| 38 | float32 result; |
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| 39 | |||
| 40 | result.f = 0; |
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| 41 | |||
| 42 | expdiff=a.parts.exp - b.parts.exp; |
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| 43 | if ((expdiff<0)||((expdiff==0)&&(a.parts.mantisa<b.parts.mantisa))) { |
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| 44 | if (isFloat32NaN(b)) { |
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| 45 | //TODO: fix SigNaN |
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| 46 | if (isFloat32SigNaN(b)) { |
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| 47 | }; |
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| 48 | return b; |
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| 49 | }; |
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| 50 | |||
| 51 | if (b.parts.exp==0xFF) { |
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| 52 | b.parts.sign=!b.parts.sign; /* num -(+-inf) = -+inf */ |
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| 53 | return b; |
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| 54 | } |
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| 55 | |||
| 56 | result.parts.sign = !a.parts.sign; |
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| 57 | |||
| 58 | mant1=b.parts.mantisa; |
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| 59 | exp1=b.parts.exp; |
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| 60 | mant2=a.parts.mantisa; |
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| 61 | exp2=a.parts.exp; |
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| 62 | expdiff*=-1; |
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| 63 | } else { |
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| 64 | if (isFloat32NaN(a)) { |
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| 65 | //TODO: fix SigNaN |
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| 66 | if ((isFloat32SigNaN(a))||(isFloat32SigNaN(b))) { |
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| 67 | }; |
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| 68 | return a; |
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| 69 | }; |
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| 70 | |||
| 71 | if (a.parts.exp==0xFF) { |
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| 72 | if (b.parts.exp==0xFF) { |
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| 73 | /* inf - inf => nan */ |
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| 74 | //TODO: fix exception |
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| 75 | result.binary = FLOAT32_NAN; |
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| 76 | return result; |
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| 77 | }; |
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| 78 | return a; |
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| 79 | } |
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| 80 | |||
| 81 | result.parts.sign = a.parts.sign; |
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| 82 | |||
| 83 | mant1=a.parts.mantisa; |
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| 84 | exp1=a.parts.exp; |
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| 85 | mant2=b.parts.mantisa; |
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| 86 | exp2=b.parts.exp; |
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| 87 | }; |
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| 88 | |||
| 89 | if (exp1==0) { |
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| 90 | //both are denormalized |
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| 91 | result.parts.mantisa=mant1-mant2; |
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| 92 | if (result.parts.mantisa>mant1) { |
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| 93 | //TODO: underflow exception |
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| 94 | return result; |
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| 95 | }; |
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| 96 | result.parts.exp=0; |
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| 97 | return result; |
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| 98 | }; |
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| 99 | |||
| 100 | // create some space for rounding |
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| 101 | mant1<<=6; |
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| 102 | mant2<<=6; |
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| 103 | |||
| 104 | mant1|=0x20000000; //add hidden bit |
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| 105 | |||
| 106 | |||
| 107 | if (exp2==0) { |
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| 108 | --expdiff; |
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| 109 | } else { |
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| 110 | mant2|=0x20000000; //hidden bit |
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| 111 | }; |
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| 112 | |||
| 113 | if (expdiff>24) { |
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| 114 | goto done; |
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| 115 | }; |
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| 116 | |||
| 117 | mant1 = mant1-(mant2>>expdiff); |
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| 118 | done: |
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| 119 | //TODO: find first nonzero digit and shift result and detect possibly underflow |
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| 120 | while ((exp1>0)&&(!(mant1&0x20000000))) { |
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| 121 | exp1--; |
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| 122 | mant1 <<= 1; |
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| 123 | /* TODO: fix underflow - mant1 == 0 does not necessary means underflow... */ |
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| 124 | }; |
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| 125 | |||
| 126 | //rounding - if first bit after mantisa is set then round up |
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| 127 | mant1 += 0x20; |
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| 128 | |||
| 129 | if (mant1&0x40000000) { |
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| 130 | ++exp1; |
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| 131 | mant1>>=1; |
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| 132 | }; |
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| 133 | |||
| 134 | result.parts.mantisa = ((mant1&(~0x20000000))>>6); /*Clear hidden bit and shift */ |
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| 135 | result.parts.exp = exp1; |
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| 136 | |||
| 137 | return result; |
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| 138 | }; |
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| 139 |