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477
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1 * Add for REAL #'s - 6309 version
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2 L3FB1 pshs x Preserve X
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3 tst 2,y 1st byte of mantissa 0 (means value is 0)?
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4 beq L3FC7 Yes, eat temp var & leave other var alone
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5 tst 8,y Is original # a 0?
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6 bne L3FCB No, go do actual add
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7 L3FBB ldq 1,y Get Exponent & 1st 3 bytes of mantissa
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8 stq 7,y Save in destination var space
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9 lda 5,y Copy last byte of mantissa (sign bit) to orig var
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10 sta $B,y
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11 L3FC7 leay 6,y Eat temp var & return
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12 puls pc,x
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13
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14 * Real add with non-zero values starts here
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15 * NOTE: Exponents are 2^n, with n being the SIGNED exponent byte
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16 L3FCB lda 7,y Get 1st exponent
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17 suba 1,y Calculate difference in exponents
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18 bvc L3FD5 Didn't exceed +127 or -128, skip ahead
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19 bpl L3FBB Went too big on plus side, make temp var the answe
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20 bra L3FC7 Too small, eat temp var & leave answer alone
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21
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22 L3FD5 bmi L3FDD If negative difference in exponents, skip ahead
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23 cmpa #31 Difference of exponents within 0-31?
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24 ble L3FE5 Yes, go deal with it
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25 bra L3FC7 >2^31, out of range so eat temp var & return
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26
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27 L3FDD cmpa #-31 Difference of exponents within -1 to -31?
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28 blt L3FBB <2^-31, out of range so copy temp to answer
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29 ldb 1,y ???Since negative difference, copy temp exponent
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30 stb 7,y overtop destination exponent?
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31 * As of this point, exponent in temp var no longer needed (A=difference in exp
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32 L3FE5 ldb $B,y Get sign of dest. var
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33 andb #$01 Keep sign bit only
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34 stb ,y Save copy over var type
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35 eorb 5,y EOR with sign bit of temp var
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36 andb #$01 Keep only merged sign bit
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37 stb 1,y Save what resulting sign should be
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38 * aim #$fe,$B,y Force sign bit off on dest var
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39 * aim #$fe,5,y Force sign bit off on temp var
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40 fcb $62,$fe,$2b
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41 fcb $62,$fe,$25
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42 tsta Are exponents exactly the same?
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43 beq L4031 Yes, skip ahead
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44 bpl L4029 Exponent difference positive, go process
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45 * Exponent difference is a negative value
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46 nega Force to positive
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47 leax 6,y Point X to dest. var
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48 bsr L4082 Shift mantissa to match other value (into X:D)
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49 tst 1,y Result going to be positive?
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50 beq L4039 Yes, skip ahead
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51 L400B subw 4,y Q=Q-[2,y]
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52 sbcd 2,y
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53 bcc L404D No borrow required, skip ahead
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54 comw Do NEGQ
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55 comd
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56 addw #1
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57 adcd #0
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58 L4025 dec ,y Drop exponent by 1
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59 bra L404D
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60
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61 * >24 bits to shift - Just use B, then clear a, tfr d to w, clrd
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62 Shift24 beq SkpSh24 Even byte, skip ahead
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63 ldb 2,x Get MSB of # to shift
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64 S24Lp lsrb Shift it down
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65 deca Until done
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66 bne S24Lp
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67 tfr d,w Copy to LSW
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68 clrb Clear out MSW
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69 rts
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70
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71 * Exactly 24 bits
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72 SkpSh24 ldf 2,x Get LSB
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73 clre Clear 2nd LSB
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74 clrb Clear MS 24 bits (A=0 to get here)
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75 rts
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76
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77 * Exponent difference is positive value
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78 L4029 leax ,y Point X to temp var
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79 bsr L4082 Shift mantissa to match other value
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80 stq 2,y Save shifted result
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81 * Equal exponents come here
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82 L4031 ldq 8,y Get mantissa of dest var into Q
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83 tst 1,y Check exponent of temp var
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84 bne L400B <>0, go do Subtract again
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85 L4039 addw 4,y 32 bit add of Q+[2,y]
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86 adcd 2,y
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87 bcc L404D No overflow carry after add, skip ahead
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88 rord Overflow, divide 32 bit mantissa by 2
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89 rorw
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90 inc 7,y Bump up exponent of dest var by 1
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91 L404D tsta Check sign of MSb of Q
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92 bmi L4060 Set, skip ahead
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93 andcc #^Carry Force carry bit off (for ROLW since no LSLW)
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94 L4050 dec 7,y Drop exponent of dest var by 1
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95 bvc L4054 Not underflowed, continue
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96 puls x Pull X back before zeroing out answer
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97 bra L40DD Underflow; answer=0
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98
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99 L4054 rolw 32 bit multiply by 2
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100 rold
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101 bpl L4050 Keep doing until a set bit comes out
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102 L4060 addw #1 Add 1 to Q
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103 adcd #0
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104 bcc L4071 No carry, skip ahead
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105 rora
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106 inc 7,y
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107 L4071 std 8,y Save MSW of answer
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108 tfr w,d Move LSW to D
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109 lsrb Eat sign bit
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110 lslb
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111 orb ,y Put in sign of result
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112 L407C std $A,y Save LSW with sign bit
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113 leay 6,y Eat temp var
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114 puls pc,x Restore X & return
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115
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116 * Tested:WORKS
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117 * ENTRY: A=ABS(difference between exponents) - will never be 0?
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118 * Y=Ptr to var packet 1
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119 * X=Ptr to var packet 2
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120 * During: Q=32 bit mantissa
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121 * <u0014 = ABS difference of exponents
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122 * Exit: Q:32 bit shifted mantissa
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123 L4082 suba #24 24-31 bit shift?
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124 bge Shift24 Yes, go process
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125 adda #8 16-23 bit shift?
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126 bge Shift16 Yes, go process
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127 adda #8 8-15 bit shift?
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128 bge Shift8 Yes, go process
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129 adda #8 Restore 1-7 bit shift count
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130 sta <u0014 Save # of shifts required (1-7)
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131 ldq 2,x Get # to shift
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132 L40BD lsrd Shift 32 bit # (worst case is 180 cycles)
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133 rorw
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134 dec <u0014 Dec # shifts left to do
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135 bne L40BD Keep doing until done
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136 rts
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137
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138 * >15 bits to shift
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139 Shift16 beq SkpSh16 Even 2 bytes, go do
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140 ldw 2,x Get MSW of # to shift
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141 S16Lp lsrw Shift it down (worst case is 90 cycles)
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142 deca Until done
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143 bne S16Lp
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144 clrb Clear MSW of Q (A=0 from dec loop)
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145 rts
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146
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147 * Exactly 16 bits
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148 SkpSh16 ldw 2,x Get LSW of Q
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149 clrb
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150 rts
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151
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152 * >7 bits to shift - Use B:W
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153 Shift8 beq SkpSh8 Exactly 8, use faster method
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154 ldb 2,x Get LS 24 bits
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155 ldw 3,x
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156 S8Lp lsrb Shift it down
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157 rorw
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158 deca
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159 bne S8Lp
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160 rts
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161
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162 * Exactly 8 bits (A=0 to get here)
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163 SkpSh8 ldb 2,x Get MSW of Q
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164 ldw 3,x Get LSW of Q
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165 rts
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