Routines |
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The address of this routine is found in the table of addresses.
This subroutine gives a 'last value' on the top of the calculator stack that is the result of converting a number given in the form xEm, where m is a positive or negative integer. The subroutine is entered with x at the top of the calculator stack and m in the A register.
The method used is to find the absolute value of m, say p, and to multiply or divide x by 10↑p according to whether m is positive or negative.
To achieve this, p is shifted right until it is zero, and x is multiplied or divided by 10↑(2↑n) for each set bit b(n) of p. Since p is never much more than 39, bits 6 and 7 of p will not normally be set.
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e_to_fp | 2D4F | RLCA | Test the sign of m by rotating bit 7 of A into the carry without changing A. | |||||
2D50 | RRCA | |||||||
2D51 | JR NC,E_SAVE | Jump if m is positive. | ||||||
2D53 | CPL | Negate m in A without disturbing the carry flag. | ||||||
2D54 | INC A | |||||||
E_SAVE | 2D55 | PUSH AF | Save m in A briefly. | |||||
2D56 | LD HL,$5C92 | This is MEMBOT; a sign flag is now stored in the first byte of mem-0, i.e. 0 for '+' and 1 for '-'. | ||||||
2D59 | CALL FP_0_1 | |||||||
2D5C | RST $28 | The stack holds x. | ||||||
2D5D | DEFB $A4 | stk_ten: x, 10 | ||||||
2D5E | DEFB $38 | end_calc: x, 10 | ||||||
2D5F | POP AF | Restore m in A. | ||||||
E_LOOP | 2D60 | SRL A | In the loop, shift out the next bit of m, modifying the carry and zero flags appropriately; jump if carry reset. | |||||
2D62 | JR NC,E_TST_END | |||||||
2D64 | PUSH AF | Save the rest of m and the flags. | ||||||
2D65 | RST $28 | The stack holds x' and 10↑(2↑n), where x' is an interim stage in the multiplication of x by 10↑m, and n=0, 1, 2, 3, 4 or 5. | ||||||
2D66 | DEFB $C1 | st_mem_1: (10↑(2↑n) is copied to mem-1) | ||||||
2D67 | DEFB $E0 | get_mem_0: x', 10↑(2↑n), (1/0) | ||||||
2D68 | DEFB $00 | jump_true to E_DIVSN: x', 10↑(2↑n) | ||||||
2D69 | DEFB $04 | |||||||
2D6A | DEFB $04 | multiply: x'*10↑(2↑n)=x" | ||||||
2D6B | DEFB $33 | jump to E_FETCH: x'' | ||||||
2D6C | DEFB $02 | |||||||
E_DIVSN | 2D6D | DEFB $05 | division: x/10↑(2↑n)=x'' (x'' is x'*10↑(2↑n) or x'/10↑(2↑n) according as m is '+' or '-') | |||||
E_FETCH | 2D6E | DEFB $E1 | get_mem_1: x'', 10↑(2↑n) | |||||
2D6F | DEFB $38 | end_calc: x'', 10↑(2↑n) | ||||||
2D70 | POP AF | Restore the rest of m in A, and the flags. | ||||||
E_TST_END | 2D71 | JR Z,E_END | Jump if m has been reduced to zero. | |||||
2D73 | PUSH AF | Save the rest of m in A. | ||||||
2D74 | RST $28 | x'', 10↑(2↑n) | ||||||
2D75 | DEFB $31 | duplicate: x'', 10↑(2↑n), 10↑(2↑n) | ||||||
2D76 | DEFB $04 | multiply: x'', 10↑(2↑(n+1)) | ||||||
2D77 | DEFB $38 | end_calc: x'', 10↑(2↑(n+1)) | ||||||
2D78 | POP AF | Restore the rest of m in A. | ||||||
2D79 | JR E_LOOP | Jump back for all bits of m. | ||||||
E_END | 2D7B | RST $28 | Use the calculator to delete the final power of 10 reached leaving the 'last value' x*10↑m on the stack. | |||||
2D7C | DEFB $02 | delete | ||||||
2D7D | DEFB $38 | end_calc | ||||||
2D7E | RET |
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