hw4

.MODEL SMALL
.STACK 100h
.DATA

e       DW ?
eSign   DW ?
k       DW ?
zero    DQ 0.0
ten     DQ 10.0
tenword DW 10
one     DQ 1.0

.CODE
.386
.387

PUBLIC _myftoa
;extern void myftoa(double f, char str[])
;                   [BP+4]      [BP+12]
_myftoa PROC NEAR
    PUSH BP
    MOV BP, SP
    PUSH DI
    PUSH SI

;intiate variables
    MOV e, 0
    MOV DI, [BP+12]
    MOV SI,[BP+12]
    MOV eSign, 0
    ;save f=[BP+2]
    FLD QWORD PTR [BP+4]

 ;initiate str with '0'
    MOV CX,12
    strZero:
    MOV [DI],BYTE PTR '0'
    INC DI
    LOOP strZero

    MOV DI, [BP+12]

;check if f=0, if yes- set the string as needed
    FTST
    FSTSW AX
    SAHF
    JNE fIsNOtZero
    MOV [SI], BYTE PTR ' '
    MOV [SI+2],BYTE PTR '.'
    MOV [SI+8],BYTE PTR 'e'
    MOV [SI+9],BYTE PTR '+'
    JMP sof
fIsNOtZero:
;check and save sign by comparing f and 0
    FTST
    FSTSW AX
    SAHF
    JA checkrange
    MOV [DI],BYTE PTR '-'
    ADD DI, 1
    FABS

;check f's range, above 10 or lower than 1
checkrange:
    FCOM ten
    FSTSW AX
    SAHF
    JAE divLoop
    FCOM one
    FSTSW AX
    SAHF
    JB mulLoop
    JMP fIsNormal
;if f>=10.0
divLoop:
    FDIV ten
    INC e
    FCOM ten
    FSTSW AX
    SAHF
    JAE divLoop
    MOV eSign, 1
    JMP fIsNormal

;if f<1.0
mulLoop:
    FMUL ten
    INC e
    FCOM one
    FSTSW AX
    SAHF
    JB mulLoop

; in this point, f is between 1.0 and 10.0
fIsNormal:
    MOV BX, 0
; insert normal f into the string using the algorithem requested
strInsertLoop:
    FLD zero
    MOV k,0
kLoop:
    FADD one
    INC k
    FCOM
    FSTSW AX
    SAHF
    JB kLoop
    DEC k ;k=k-1
    MOV CX, k
    ADD CX, '0'
    MOV [DI+BX],CX
    CMP BX, 0
    JNE notfirsttime
    INC DI
    MOV [DI], BYTE PTR '.' ; after the first char insert '.'
notfirsttime:
    FSUB one
    FSUB
    FMUL ten
    INC BX
    CMP BX, 6
    JB strInsertLoop

    MOV [DI+BX],BYTE PTR 'e'
    INC BX

    CMP eSign, 0
    JNE ePos
    MOV [DI+BX],BYTE PTR '-'
    JMP enterE
ePos:
    MOV [DI+BX],BYTE PTR '+'

;at last- enter the digits of e (1/2 digits)
enterE:
    MOV AX, e
    MOV DX, 0
    DIV tenword
    ADD AX, '0'
    INC BX
    MOV [DI+BX],AX
    ADD DX, '0'
    INC BX
    MOV [DI+BX],DX


sof:
    FFREE
    POP SI
    POP DI
    POP BP
    RET
_myftoa ENDP
END