| Routines

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.