Routines 
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This subroutine shifts a floatingpoint number up to 32 places right to line it up properly for addition. The number with the smaller exponent has been put in the addend position before this subroutine is called. Any overflow to the right, into the carry, is added back into the number. If the exponent difference is greater than 32, or the carry ripples right back to the beginning of the number then the number is set to zero so that the addition will not alter the other number (the augend).


SHIFT_FP  2FDD  AND A  If the exponent difference is zero, the subroutine returns at once.  
2FDE  RET Z  
2FDF  CP $21  If the difference is greater than +20, jump forward.  
2FE1  JR NC,ADDEND_0  
2FE3  PUSH BC  Save BC briefly.  
2FE4  LD B,A  Transfer the exponent difference to B to count the shifts right.  
ONE_SHIFT  2FE5  EXX  Arithmetic shift right for L', preserving the sign marker bits.  
2FE6  SRA L  
2FE8  RR D  Rotate right with carry D', E', D and E, thereby shifting the whole five bytes of the number to the right as many times as B counts.  
2FEA  RR E  
2FEC  EXX  
2FED  RR D  
2FEF  RR E  
2FF1  DJNZ ONE_SHIFT  Loop back until B reaches zero.  
2FF3  POP BC  Restore the original BC.  
2FF4  RET NC  Done if no carry to retrieve.  
2FF5  CALL ADD_BACK  Retrieve carry.  
2FF8  RET NZ  Return unless the carry rippled right back. (In this case there is nothing to add.)  
ADDEND_0  2FF9  EXX  Fetch L', D' and E'.  
2FFA  XOR A  Clear the A register.  
This entry point is used by the routine at multiply.


ZEROS_4_5  2FFB  LD L,$00  Set the addend to zero in D', E', D and E, together with its marker byte (sign indicator) L', which was +00 for a positive number and +FF for a negative number. This produces only 4 zero bytes when called for near underflow by multiply.  
2FFD  LD D,A  
2FFE  LD E,L  
2FFF  EXX  
3000  LD DE,$0000  
3003  RET  Finished. 
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