Routines
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10956: THE 'INT-EXP' SUBROUTINE
Used by the routines at STK_VAR and DIM.
This subroutine returns the result of evaluating the 'next expression' as an integer value held in the BC register pair. The subroutine also tests this result against a limit-value supplied in the HL register pair. The carry flag becomes set if there is an 'out of range' error.
The A register is used as an 'error register' and holds 0 if there is no 'previous error' and 255 if there has been one.
Input
HL Limit value
Output
BC Expression value
F Carry flag set if this value is out of range
INT_EXP1 10956 XOR A Clear the 'error register'.
This entry point is used by the routine at SLICING.
INT_EXP2 10957 PUSH DE Save both the DE and HL register pairs throughout.
10958 PUSH HL
10959 PUSH AF Save the 'error register' briefly.
10960 CALL CLASS_06 The 'next expression' is evaluated to give a 'last value' on the calculator stack.
10963 POP AF Restore the 'error register'.
10964 CALL SYNTAX_Z Jump forward if checking syntax.
10967 JR Z,I_RESTORE
10969 PUSH AF Save the error register again.
10970 CALL FIND_INT2 The 'last value' is compressed Into BC.
10973 POP DE Error register to D.
10974 LD A,B A 'next expression' that gives zero is always in error so jump forward if it is so.
10975 OR C
10976 SCF
10977 JR Z,I_CARRY
10979 POP HL Take a copy of the limit-value. This will be a 'dimension-size', a 'DIM-limit' or a 'string length'.
10980 PUSH HL
10981 AND A Now compare the result of evaluating the expression against the limit.
10982 SBC HL,BC
The state of the carry flag and the value held in the D register are now manipulated so as to give the appropriate value for the 'error register'.
I_CARRY 10984 LD A,D Fetch the 'old error value'.
10985 SBC A,0 Form the 'new error value': 0 if no error at any time, 255 or less if an 'out of range' error on this pass or on previous ones.
Restore the registers before returning.
I_RESTORE 10987 POP HL Restore HL and DE.
10988 POP DE
10989 RET Return; 'error register' is the A register.
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