Routine:        Fpint   
Function:       Converts a floating point number to a two byte integer. The FP number must be positive and <65536.
Called by:      Measno, Visc
Calls:          Error
Entry:          IX points to FP number
Exit:           HL holds the integer part
Preserved:      None


FPINT   LD      B,(IX+4)
        LD      D,(IX+3)
        LD      E,(IX+2)
        LD      H,(IX+1)
        LD      L,(IX)
        LD      A,B
; Read the floating point number into the Z80 registers.
        CP      17
        JR      C,FPINT1
        CP      128
        JR      C,FPINT4
; If the floating point number is too big then jump to fpint4 and signal error code 6; otherwise if it is zero, set HL to zero and return. 
        LD      L,0
        LD      H,L
        RET
FPINT1  BIT     7,D
        JR      NZ,FPINT5
; If negative, signal error 7. The rest of the routine is just shifting until the exponent becomes zero.
        INC     B
        XOR     A
        LD      C,A
        SET     7,D
        JR      FPINT3
FPINT2  RL      L
        RL      H
        RL      E
        EL      D
        RL      C
        RL      A
FPINT3  DJNZ    FPINT2
; Load the integer part of the floating point number into HL, and return.
        LD      L,C
        LD      H,A
        RET
FPINT4  LD      A,6

        CALL    ERROR
        RET
FPINT5  LD      A,7
        CALL    ERROR
        RET