WinCMOC (M6809 C Compiler) Code

// By Pierre Sarrazin <http://sarrazip.com/>.
// This file is in the public domain.
//
// Converted to C for WinCMOC by Derek Evans 2016

#include "_cmoc.h"

/*
* Multiples w by b to obtain a 24-bit product.
* Stores the high byte of the product in *productHi,
* and returns the low word of the product.
*/

asm word mulwb(byte* productHi, word w, byte b)
{
    asm {
        pshs    u
        tfr     s,u
        ldx     6,u                             // load w
        ldb     9,u                             // load b
        bsr     MUL168_TO24
        pshs    x                               // preserve low word of product
        ldx     4,u                             // get productHi pointer
        stb     ,x                              // return high byte of product
        puls    a,b                             // retrieve and return low word of product
        tfr     u,s
        puls    u,pc

        //MUL168_TO24: EXPORT

        MUL168_TO24:
        pshs    x,b,a
        clr     ,-s                             // allocate 3 bytes to store 24-bit product
        clr     ,-s
        clr     ,-s
        lda     6,s                             // low byte of X
        mul
        std     1,s                             // low 16-bit of 24-bit storage
        ldd     4,s                             // original B in A, high byte of X in B
        mul
        addd    ,s                              // add D to high 16 bits of storage
        std     ,s
        ldb     ,s
        ldx     1,s
        lda     3,s                             // restore orignal A
        leas    7,s
    }
}