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359C: THE 'STRING CONCATENATION' OPERATION (offset +17)
The address of this routine is found in the table of addresses. It is called indirectly via fp_calc_2.
This subroutine performs the binary operation 'A$+B$'. The parameters for these strings are fetched and the total length found. Sufficient room to hold both the strings is made available in the work space and the strings are copied over. The result of this subroutine is therefore to produce a temporary variable A$+B$ that resides in the work space.
Input
Output
strs_add 359C CALL STK_FETCH The parameters of the second string are fetched and saved.
359F PUSH DE
35A0 PUSH BC
35A1 CALL STK_FETCH The parameters of the first string are fetched.
35A4 POP HL The lengths are now in HL and BC.
35A5 PUSH HL
35A6 PUSH DE The parameters of the first string are saved.
35A7 PUSH BC
35A8 ADD HL,BC The total length of the two strings is calculated and passed to BC.
35A9 LD B,H
35AA LD C,L
35AB RST $30 Sufficient room is made available.
35AC CALL STK_STO The parameters of the new string are passed to the calculator stack.
35AF POP BC The parameters of the first string are retrieved and the string copied to the work space as long as it is not a null string.
35B0 POP HL
35B1 LD A,B
35B2 OR C
35B3 JR Z,OTHER_STR
35B5 LDIR
OTHER_STR 35B7 POP BC Exactly the same procedure is followed for the second string thereby giving 'A$+B$'.
35B8 POP HL
35B9 LD A,B
35BA OR C
35BB JR Z,STK_PNTRS
35BD LDIR
This routine continues into STK_PNTRS.
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