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477
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1 * Main routine for REAL multiply - 6309 version
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2 * 08/07/95 - Change L40DD to use CLRD/CLRW/STQ (Saves 1 cycle)
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3 * - Changed entire routine as per Chris Dekker's RunB
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4 * 08/08/95 - Took out PSHS/PULS X
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5 L40D3 lda 2,y Get 1st byte of mantissa
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6 bpl L40DD If mantissa is in lower range, force result to 0
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7 lda 8,y Get 1st byte of mantissa from 2nd number
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8 bmi L40E9 If in upper range, go do multiply
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9 L40DD clrd Force REAL result to 0
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10 clrw
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11 stq 7,y Save 0 as result
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12 sta $B,y
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13 leay 6,y Eat temp var & return
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14 rts
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15
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16 * Check for possible over/underflows before doing multiply
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17 L40E9 lda 1,y Get exponent from temp var
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18 adda 7,y Add to exponent from 1st var
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19 bvc L40F6 If within 8 bit range, go do multiply
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20 L40EF bpl L40DD If resulting exponent is too small, result=0
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21 comb Resulting exponent too big, exit with
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22 ldb #$32 Floating overflow error
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23 rts
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24
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25 * Exponent possibly in range, process
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26 L40F6 sta 7,y Save resultant exponent overtop 1st vars
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27 ldb $B,y Get sign bit of 2nd #
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28 eorb 5,y EOR with sign bit of 1st #
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29 andb #$01 Only keep resulting sign bit
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30 stb ,y Save what sign of result will be
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31 lda $B,y Now, for actual multiply, force to positive
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32 anda #$FE
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33 sta $B,y
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34 ldb 5,y Force both mantissa's to positive
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35 andb #$FE
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36 stb 5,y
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37 * Possible 32x32 bit multiply routine?
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38 mul Multiply LSB's together
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39 clre
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40 clr <u0014 Clear out 3rd byte to keep track of
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41 tfr a,f Save MSB into middle byte
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42 lda $B,y LSB * 2nd LSB
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43 ldb 4,y
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44 mul
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45 addr d,w Add to previous #
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46 bcc L4120 No carry required, skip ahead
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47 inc <u0014
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48 L4120 lda $A,y 2nd LSB * LSB
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49 ldb 5,y
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50 mul
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51 addr d,w Add to previous #
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52 bcc L412D
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53 inc <u0014
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54 L412D tfr e,f
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55 lde <u0014
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56 clr <u0014
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57 lda $B,y
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58 ldb 3,y
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59 mul
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60 addr d,w Add to previous #
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61 bcc L4142
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62 inc <u0014
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63 L4142 lda $A,y
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64 ldb 4,y
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65 mul
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66 addr d,w Add to previous #
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67 bcc L414F
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68 inc <u0014
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69 L414F lda 9,y
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70 ldb 5,y
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71 mul
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72 addr d,w Add to previous #
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73 bcc L415C
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74 inc <u0014
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75 L415C tfr e,f
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76 lde <u0014
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77 clr <u0014
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78 lda $B,y
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79 ldb 2,y
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80 mul
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81 addr d,w Add to previous #
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82 bcc L4171
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83 inc <u0014
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84 L4171 lda $A,y
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85 ldb $3,y
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86 mul
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87 addr d,w Add to previous #
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88 bcc L417E
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89 inc <u0014
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90 L417E lda 9,y
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91 ldb 4,y
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92 mul
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93 addr d,w Add to previous #
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94 bcc L418B
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95 inc <u0014
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96 L418B lda 8,y
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97 ldb 5,y
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98 mul
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99 addr d,w Add to previous #
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100 bcc L4198
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101 inc <u0014
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102 L4198 stf $B,y
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103 tfr e,f
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104 lde <u0014
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105 clr <u0014
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106 lda $A,y
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107 ldb 2,y
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108 mul
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109 addr d,w Add to previous #
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110 bcc L41AF
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111 inc <u0014
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112 L41AF lda 9,y
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113 ldb 3,y
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114 mul
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115 addr d,w Add to previous #
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116 bcc L41BC
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117 inc <u0014
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118 L41BC lda 8,y
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119 ldb 4,y
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120 mul
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121 addr d,w Add to previous #
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122 bcc L41C9
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123 inc <u0014
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124 L41C9 stf $A,y
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125 tfr e,f
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126 lde <u0014
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127 clr <u0014
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128 lda 9,y
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129 ldb 2,y
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130 mul
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131 addr d,w Add to previous #
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132 bcc L41E0
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133 inc <u0014
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134 L41E0 lda 8,y
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135 ldb 3,y
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136 mul
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137 addr d,w Add to previous #
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138 bcc L41ED
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139 inc <u0014
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140 L41ED lda 8,y
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141 ldb 2,y
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142 mul
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143 tfr w,u
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144 tfr e,f
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145 lde <u0014
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146 exg d,u
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147 addr u,w
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148 bmi L4202
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149 asl $B,y
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150 rol $A,y
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151 rolb
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152 rolw
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153 dec 7,y
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154 bvs L421B
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155
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156 L4202 tfr b,a
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157 ldb $A,y
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158 exg d,w
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159 addw #1
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160 adcd #0
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161 bne L421B
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162 rora
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163 inc 7,y
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164 L421B exg d,w
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165 lsrb Clear sign bit
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166 lslb
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167 orb ,y Merge resultant sign bit
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168 std $A,y
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169 stw 8,y
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170 leay 6,y
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171 clrb No error, restore & return
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172 rts
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