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477
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1 * Main routine for REAL multiply - 6809 version
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2 L40D3 pshs x Preserve X
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3 lda 2,y Get 1st byte of mantissa
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4 bpl L40DD If mantissa is in lower range, force result to 0
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5 lda 8,y Get 1st byte of mantissa from 2nd number
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6 bmi L40E9 If in upper range, go do multiply
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7 L40DD clra
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8 clrb
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9 std 7,y Save 0 as result
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10 std 9,y
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11 sta $B,y
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12 leay 6,y Eat temp var
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13 puls pc,x
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14
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15 * Check for possible over/underflows before doing multiply
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16 L40E9 lda 1,y Get exponent from temp var
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17 adda 7,y Add to exponent from 1st var
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18 bvc L40F6 If within 8 bit range, go do multiply
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19 L40EF bpl L40DD If resulting exponent is too small, result=0
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20 comb Resulting exponent too big, exit with
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21 ldb #$32 Floating overflow error
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22 puls pc,x
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23
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24 * Exponent possibly in range, process
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25 L40F6 sta 7,y Save resultant exponent overtop 1st vars
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26 ldb $B,y Get sign bit of 2nd #
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27 eorb 5,y EOR with sign bit of 1st #
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28 andb #$01 Only keep resulting sign bit
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29 stb ,y Save what sign of result will be
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30 lda $B,y Now, for actual multiply, force to positive
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31 anda #$FE
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32 sta $B,y
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33 ldb 5,y Force both mantissa's to positive
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34 andb #$FE
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35 stb 5,y
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36 * Possible 32x32 bit multiply routine?
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37 mul Multiply LSB's together
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38 sta ,-s Save MSB of result only (drop LSB)
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39 clr ,-s And make 2 zero hi-bytes (result is 3 byte #)
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40 clr ,-s
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41 lda $B,y LSB * 2nd LSB
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42 ldb 4,y
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43 mul
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44 addd 1,s Add to previous #
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45 std 1,s
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46 bcc L4120 No carry required, skip ahead
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47 inc ,s
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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 addd 1,s Add with carry to previous #
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52 std 1,s
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53 bcc L412D
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54 inc ,s
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55 L412D ldx ,s Done 16x8 multiply, now just keep MSW
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56 stx 1,s
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57 clr ,s Zero out hi-byte in 3 byte #
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58 lda $B,y
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59 ldb 3,y
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60 mul
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61 addd 1,s
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62 std 1,s
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63 bcc L4142
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64 inc ,s
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65 L4142 lda $0A,y
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66 ldb $04,y
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67 mul
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68 addd $01,s
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69 std $01,s
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70 bcc L414F
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71 inc ,s
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72 L414F lda $09,y
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73 ldb $05,y
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74 mul
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75 addd 1,s
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76 std 1,s
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77 bcc L415C
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78 inc ,s
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79 L415C ldb 2,s
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80 ldx ,s
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81 stx 1,s
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82 clr ,s
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83 lda $B,y
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84 ldb $2,y
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85 mul
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86 addd 1,s
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87 std 1,s
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88 bhs L4171
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89 inc ,s
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90 L4171 lda $A,y
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91 ldb $3,y
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92 mul
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93 addd 1,s
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94 std 1,s
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95 bhs L417E
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96 inc ,s
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97 L417E lda 9,y
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98 ldb 4,y
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99 mul
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100 addd 1,s
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101 std 1,s
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102 bhs L418B
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103 inc ,s
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104 L418B lda $08,y
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105 ldb $05,y
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106 mul
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107 addd $01,s
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108 std $01,s
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109 bhs L4198
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110 inc ,s
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111 L4198 ldb $02,s
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112 ldx ,s
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113 stx $01,s
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114 clr ,s
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115 stb $0B,y
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116 lda $0A,y
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117 ldb $02,y
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118 mul
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119 addd $01,s
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120 std $01,s
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121 bcc L41AF
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122 inc ,s
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123 L41AF lda $09,y
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124 ldb $03,y
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125 mul
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126 addd $01,s
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127 std $01,s
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128 bcc L41BC
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129 inc ,s
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130 L41BC lda $08,y
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131 ldb $04,y
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132 mul
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133 addd $01,s
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134 std $01,s
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135 bcc L41C9
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136 inc ,s
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137 L41C9 ldb $02,s
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138 ldx ,s
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139 stx $01,s
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140 clr ,s
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141 stb $0A,y
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142 lda $09,y
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143 ldb $02,y
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144 mul
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145 addd $01,s
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146 std $01,s
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147 bcc L41E0
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148 inc ,s
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149 L41E0 lda $08,y
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150 ldb $03,y
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151 mul
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152 addd $01,s
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153 std $01,s
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154 bcc L41ED
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155 inc ,s
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156 L41ED lda $08,y
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157 ldb $02,y
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158 mul
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159 addd ,s
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160 bmi L4202
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161 lsl $0B,y
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162 rol $0A,y
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163 rol $02,s
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164 rolb
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165 rola
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166 dec 7,y
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167 bvs L421B
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168 L4202 std 8,y
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169 lda 2,s
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170 ldb $A,y
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171 addd #$0001
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172 bcc L4220
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173 inc 9,y
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174 bne L4222
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175 inc 8,y
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176 bne L4222
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177 ror 8,y
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178 inc 7,y
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179 bvc L4222
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180 L421B leas 3,s
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181 lbra L40EF
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182
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183 L4220 andb #$FE
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184 L4222 orb ,y
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185 std $A,y
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186 leay 6,y
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187 leas 3,s
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188 clrb No error, restore & return
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189 puls pc,x
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