source: xtideuniversalbios/tags/XTIDE_Universal_BIOS_v1.1.3/Src/Libraries/math.asm@ 519

; File name     :   math.asm
; Project name  :   Math library
; Created date  :   7.10.2009
; Last update   :   1.1.2010
; Author        :   Tomi Tilli
; Description   :   ASM library to for math related functions.      

;--------------- Equates -----------------------------

; String library function to include
;%define USE_MATH_MULDWBYW      ; Math_MulDWbyW
%define USE_MATH_DIVDWBYW       ; Math_DivDWbyW
%define USE_MATH_REMTOTENTHS    ; Math_RemToTenths


;-------------- Private global variables -------------
; Section containing initialized data
;SECTION .data


;-------------- Public functions ---------------------
; Section containing code
SECTION .text


;--------------------------------------------------------------------
; Macro to select lesser of two unsigned operands.
; 
; MIN_U
;   Parameters:
;       %1:     Operand 1
;       %2:     Operand 2
;   Returns:
;       %1:     Lesser unsigned operand
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%macro MIN_U 2
    cmp     %1, %2              ; Is %1 smaller?
    jb      %%Return            ;  If so, return
    mov     %1, %2              ; Copy %2 to %1
ALIGN JUMP_ALIGN
%%Return:
%endmacro


;--------------------------------------------------------------------
; Macro to select greater of two unsigned operands.
; 
; MAX_U
;   Parameters:
;       %1:     Operand 1
;       %2:     Operand 2
;   Returns:
;       %1:     Greater unsigned operand
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%macro MAX_U 2
    cmp     %1, %2              ; Is %1 greater?
    ja      %%Return            ;  If so, return
    mov     %1, %2              ; Copy %2 to %1
ALIGN JUMP_ALIGN
%%Return:
%endmacro


;--------------------------------------------------------------------
; Macro to select lesser and greater of two unsigned operands.
; 
; MINMAX_U
;   Parameters:
;       %1:     Operand 1
;       %2:     Operand 2
;   Returns:
;       %1:     Lesser unsigned operand
;       %2:     Greater unsigned operand
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%macro MINMAX_U 2
    cmp     %1, %2              ; Is %1 smaller?
    jbe     %%Return            ;  If so, return
    xchg    %1, %2              ; Exchange operands
ALIGN JUMP_ALIGN
%%Return:
%endmacro


;--------------------------------------------------------------------
; DWORD * WORD multiplication.
; Multiplies unsigned 32-bit integer by unsigned 16-bit integer.
; Result is unsigned 32-bit integer, so overflow is possible.
; 
; Math_MulDWbyW
;   Parameters:
;       DX:AX:  32-bit unsigned integer to multiply
;       CX:     16-bit unsigned multiplier
;   Returns:
;       DX:AX:  32-bit unsigned integer
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%ifdef USE_MATH_MULDWBYW
ALIGN JUMP_ALIGN
Math_MulDWbyW:
    jcxz    .RetZero            ; If CX=0, return 0
    push    bx
    mov     bx, dx              ; Copy hiword to BX
    xor     dx, dx              ; Zero DX for multiplication
    mul     cx                  ; DX:AX = AX (loword) * CX (multiplier)
    push    dx                  ; Push possible overflow
    xchg    ax, bx              ; => AX=old hiword, BX=new loword
    xor     dx, dx              ; Zero DX for division
    mul     cx                  ; DX:AX = AX (hiword) * CX (multiplier)
    pop     dx                  ; Pop possible overflow from first mul
    add     dx, ax              ; Add new hiword to overflow from first mul
    mov     ax, bx              ; Copy new loword to AX
    pop     bx
    ret
ALIGN JUMP_ALIGN
.RetZero:                       ; Return 0 in DX:AX
    xor     ax, ax
    xor     dx, dx
    ret
%endif


;--------------------------------------------------------------------
; Divide a 32-bit unsigned integer so that quotient can be 32-bit.
; 
; Math_DivDWbyW
;   Parameters:
;       DX:AX:  32-bit unsigned divident
;       CX:     16-bit unsigned divisor
;   Returns:
;       DX:AX:  32-bit unsigned quotient
;       BX:     16-bit unsigned remainder
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%ifdef USE_MATH_DIVDWBYW
ALIGN JUMP_ALIGN
Math_DivDWbyW:
    mov     bx, ax
    mov     ax, dx
    xor     dx, dx
    div     cx
    xchg    ax, bx
    div     cx
    xchg    dx, bx
    ret
%endif


;--------------------------------------------------------------------
; Converts remainder to tenths.
; 
; Math_RemToTenths
;   Parameters:
;       BX:     16-bit unsigned remainder
;       CX:     16-bit unsigned divisor used when calculated the remainder (max 2559)
;   Returns:
;       BX:     Remainder converted to tenths
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%ifdef USE_MATH_REMTOTENTHS
ALIGN JUMP_ALIGN
Math_RemToTenths:
    push    cx
    push    ax
    mov     ax, cx              ; Copy divisor to AX
    mov     cl, 10              ; Load 10 to CL
    div     cl                  ; AL = Divisor divided by 10
    inc     ax                  ; Increment to compensate new remainder
    xchg    ax, bx              ; AX = 16-bit remainder to convert
                                ; BL = Original divisor divided by 10
    div     bl                  ; AX = Original remainder converted to tenths
    eMOVZX  bx, al              ; Copy return value to BX
    pop     ax
    pop     cx
    ret
%endif