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Annotation of 43BSD/contrib/icon/lib/escan.c, revision 1.1.1.1

1.1       root        1: #include "../h/rt.h"
                      2: 
                      3: /*
                      4:  * escan - restore &subject and &pos at the end of a scanning expression.
                      5:  *
                      6:  *  Arguments:
                      7:  *    arg1 - value being scanned
                      8:  *    arg2 - old value of &subject
                      9:  *    arg3 - old value of &pos
                     10:  *    arg4 - result of the scanning expression
                     11:  *
                     12:  * The result of the scanning expression is dereferenced if it refers to &subject
                     13:  *  or &pos, then copied to the first argument (the last three will
                     14:  *  be popped when escan returns).  Then the previous values of &subject
                     15:  *  and &pos are restored.
                     16:  *
                     17:  * Escan suspends once it has restored the old &subject; on failure
                     18:  *  the new &subject and &pos are "unrestored", and the failure is
                     19:  *  propagated into the using clause.
                     20:  */
                     21: 
                     22: escan(nargs, arg4, arg3, arg2, arg1)
                     23: int nargs;
                     24: struct descrip arg4, arg3, arg2, arg1;
                     25:    {
                     26:    DclSave
                     27:    struct descrip tmp;
                     28: 
                     29:    SetBound;
                     30: 
                     31:    /*
                     32:     * If the result of the scanning expression is &subject or &pos,
                     33:     *  it is dereferenced.
                     34:     */
                     35:    if (arg4.type == D_VAR && (int)BLKLOC(arg1) == (int)&k_subject)
                     36:       DeRef(arg4)
                     37:    if (arg4.type == D_TVPOS)
                     38:       DeRef(arg4)
                     39: 
                     40:    /*
                     41:     * Copy the result of the scanning expression into arg1, which will
                     42:     *  be the result of the scan.
                     43:     */
                     44:    arg1 = arg4;
                     45: 
                     46:    /*
                     47:     * Swap new and old values of &subject, leaving the new value in arg2.
                     48:     */
                     49:    tmp = k_subject;
                     50:    k_subject = arg2;
                     51:    arg2 = tmp;
                     52: 
                     53:    /*
                     54:     * Swap new and old values of &pos, leaving the new value in arg3.
                     55:     */
                     56:    tmp = arg3;
                     57:    INTVAL(arg3) = k_pos;
                     58:    k_pos = INTVAL(tmp);
                     59: 
                     60:    /*
                     61:     * Suspend the value of the scanning expression.
                     62:     */
                     63:    suspend();
                     64: 
                     65:    /*
                     66:     * Upon resumption, restore the new values for &subject and &pos
                     67:     *  and fail.
                     68:     */
                     69:    k_subject = arg2;
                     70:    k_pos = INTVAL(arg3);
                     71: 
                     72:    fail();
                     73:    }

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