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Annotation of os2sdk/demos/examples/csalias/csalias.c, revision 1.1.1.2

1.1.1.2 ! root        1: /* This example illustrates the use of the following MS OS/2 function:
        !             2:  *     DosCreateCSAlias
1.1       root        3:  *
1.1.1.2 ! root        4:  * A data segment is allocated by calling DosAllocSeg. A small assembly
1.1       root        5:  * language routine is created in this data segment. An alias code selector 
1.1.1.2 ! root        6:  * for this data segment is obtained by calling DosCreateCSAlias. Using the
1.1       root        7:  * alias code selector, the routine in the data segment is called. After 
                      8:  * returning from the routine, the alias code selector and the data segment 
1.1.1.2 ! root        9:  * are freed by calling DosFreeSeg.
1.1       root       10:  *
                     11:  * This program illustrates the function - it does not do anything useful.
                     12:  * A more likely use of aliasing code to data is where the code is actually
                     13:  * generated at run time, rather than statically declared in this example.
                     14:  *
1.1.1.2 ! root       15:  * Created by Microsoft Corp. 1986
1.1       root       16:  */
                     17: 
1.1.1.2 ! root       18: #define INCL_DOSMEMMGR
        !            19: 
        !            20: #include       <os2def.h>              /* SELECTOROF and OFFSETOF macros    */
        !            21: #include       <bsedos.h>              /* MS OS/2 function declarations     */
1.1       root       22: #include       <stdio.h>               /* printf C lib function declaration */
1.1.1.2 ! root       23: 
1.1       root       24: 
                     25: #define        PRIVATE 0               /* segment will not be shared */
                     26: #define        SOMENUM 3               /*to be squared by proc in CSAlias'ed segment*/
                     27: 
1.1.1.2 ! root       28: UCHAR square[] = { /*a routine that computes the square of an integer*/
1.1       root       29:        0x55,                           /* push bp             */
                     30:        0x8b, 0xec,                     /* mov  bp,sp          */
                     31:        0x8b, 0x46, 0x06,               /* mov  ax,[bp+6]      */
                     32:        0xf7, 0xe0,                     /* mul  ax             */       
                     33:        0x8b, 0xe5,                     /* mov  sp,bp          */
                     34:        0x5d,                           /* pop  bp             */
                     35:        0xcb,                           /* retf                */
                     36:        '\0'                            /* terminate with null */
                     37: };
                     38: 
                     39: main ()
                     40: {
1.1.1.2 ! root       41:        SEL             DataSelector,   /* selector to data segment    */
1.1       root       42:                        CodeSelector;   /* alias code segment selector */
                     43:        char            *DataSeg;       /* pointer to data segemnet    */
                     44:        long            (*proc)(int);   /* pointer to a procedure      */
                     45:        long            SquareOfInt;    /* to hold square of an integer*/
                     46: 
                     47:        /* allocate a segment */
1.1.1.2 ! root       48:        DosAllocSeg (sizeof(square), &DataSelector, PRIVATE);
1.1       root       49: 
                     50:        /* construct a far pointer to the data segment */
1.1.1.2 ! root       51:        SELECTOROF(DataSeg) = DataSelector;
        !            52:        OFFSETOF(DataSeg) = 0;
1.1       root       53: 
                     54:        /* copy an assembly language procedure into the data segment */
                     55:        strcpy(DataSeg, square); 
                     56:        
                     57:        /* get a csalias selector for the data segment */
1.1.1.2 ! root       58:        DosCreateCSAlias (DataSelector, &CodeSelector);
1.1       root       59:        
                     60:        /* construct the address to the procedure in the csalias'ed segment */
1.1.1.2 ! root       61:        SELECTOROF(proc) = CodeSelector;
        !            62:        OFFSETOF(proc) = 0;
1.1       root       63: 
                     64:        /* execute the code in the csalias'ed data segment */
                     65:        if ((SquareOfInt = (*proc)(SOMENUM)) != (SOMENUM * SOMENUM))
                     66:          printf ("*** error: procedure in CSAlias'ed segment failed ***\n");
                     67: 
                     68:        /* free the alias code selector */
1.1.1.2 ! root       69:        DosFreeSeg(CodeSelector);
1.1       root       70: 
                     71:        /* free the data segment */
1.1.1.2 ! root       72:        DosFreeSeg(DataSelector);
1.1       root       73: }

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