//--------------------------------------------------------------------------
//
//  Software for MSP430 based e-meters.
//
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//
//  File: q1_15_mulq.c
//
//  Steve Underwood <steve-underwood@ti.com>
//  Texas Instruments Hong Kong Ltd.
//
//  $Id: q1_15_mulq.c,v 1.2 2003/07/28 09:48:22 XHKJAMES Exp $
//
//--------------------------------------------------------------------------
#include "io.h"

//uint16_t rndnum;
//uint16_t tpdnum;

//Q1.15 style 16x16=>16 multiply with TPD (triangular
//probability density) dithered rounding of the result.
;int16_t Q1_15_mulq(register int16_t x, register int16_t y)
    public Q1_15_mulq
    public tpd_gen

    RSEG CODE
Q1_15_mulq
#if defined(RESLO_)  &&  defined(RESHI_)  &&  defined(MPYS_)  &&  defined(OP2_)
    push.w  SR
    dint
    mov     R12,&MPYS_
    mov     R14,&OP2_
    mov     &RESHI_,R13
    mov     &RESLO_,R12
    pop.w   SR
#if 0
    //Do TPD dithering at the Q1.15 level
    add     @tpdnum,R12
    addc    #0,R13
    //Shift to Q1.15 format (i.e. the top 16 bits are returned)
    rla     R12
    rlc     R13
    mov     R13,R12
#endif
#if defined(__MSP430_HAS_MSP430X_CPU__)
    reta
#else
    ret
#endif
#else
    push.w R10
    push.w R15
    mov     R12,R15
    clr     R13
    mov     R13,R12

    mov     R13,R10
    tst     R15
    jge     booth_2
    mov     #-1,R10
    jmp     booth_2

booth_6
    add     R15,R12
    addc    R10,R13
booth_1
    rla     R15
    rlc     R10
booth_2
    rra     R14
    jc      booth_5
    jne     booth_1
    jmp     booth_4

booth_5
    sub     R15,R12
    subc    R10,R13
booth_3
    rla     R15
    rlc     R10
    rra     R14
    jnc     booth_6
    cmp     #0xFFFF,R14
    jne     booth_3

booth_4
    //Do TPD dithering at the Q1.15 level
    //add     @tpdnum,R12
    //addc    #0,R13
    //Shift to Q1.15 format (i.e. the top 16 bits are returned)
    rla     R12
    rlc     R13
    mov     R9,R12

    pop.w   R15
    pop.w   R10
#if defined(__MSP430_HAS_MSP430X_CPU__)
    reta
#else
    ret
#endif
#endif

// Use a linear congrual generator function to generate
// a TPD (triangular probability density) weighted random
// number. Adding a pair of even distribution random numbers
// will create a TPD. We can reuse an old random number in the
// generation of each new TPD value, as there should be very
// weak correlation between the numbers.
;void tpd_gen(void)
tpd_gen
#if 0
    mov     rndnum,@x1
    mov     #0,@x2
    sub     @x1,@x2     //0
    rla     @x1
    add     @x1,@x2     //1
    rla     @x1
    sub     @x1,@x2     //2
    rla     @x1
    rla     @x1
    add     @x1,@x2     //4
    rla     @x1
    rla     @x1
    sub     @x1,@x2     //6
    rla     @x1
    add     @x1,@x2     //7
    rla     @x1
    rla     @x1
    rla     @x1
    sub     @x1,@x2     //10
    add     #13489,@x2
    and     #0x3FFF,@x2
    mov     rndnum,R8
    add     @x2,R8
    mov     R8,tpdnum
    mov     @x2,rndnum
#endif
#if defined(__MSP430_HAS_MSP430X_CPU__)
    reta
#else
    ret
#endif
    end