Setjmp Library

The Setjmp library contains functions and types definitions for bypassing the normal function call and return discipline.

Library Routines

Setjmp
Longjmp

Setjmp

Prototype	function setjmp(var env : array[4] of word) : integer;
Returns	`0` if the return is from direct invocation `nonzero value` if the return is from a call to `longjmp` (this value will be set by the `longjmp` routine)
Description	This function saves calling position for a later use by longjmp. Parameters : `env:` buffer suitable for holding information needed for restoring calling environment
Requires	Nothing.
Example	var buf : array[4] of word; ... Setjmp(buf);

Longjmp

Prototype	procedure longjmp(var env : array[4] of word; val : integer);
Returns	Nothing.
Description	Restores calling environment saved in the `env` buffer by the most recent invocation of `setjmp`. If there has been no such invocation, or the function containing the invocation of setjmp has terminated in the interim, the behavior is undefined. Parameters : `env:` buffer holding the information saved by the corresponding `setjmp` invocation `val:` value to be returned by the corresponding `setjmp` function
Requires	Invocation of `longjmp` must occur before return from the function in which `setjmp` was called encounters.
Example	var buf : array[4] of word; ... Longjmp(buf, 2);

Library Example

Example demonstrates function cross calling using setjmp and longjmp functions. When called, Setjmp() saves its calling environment in its buf argument for later use by the Longjmp(). Longjmp(), on the other hand, restores the environment saved by the most recent invocation of the Setjmp() with the corresponding buf argument.

Copy Code To Clipboard

program Setjmp;

var buf : array[4] of word ;   //  Note : Program flow diagrams are indexed according
                               //  to the sequence of execution

procedure func33();            //  2<------------|
  begin                        //                |
    Delay_ms(1000);            //                |
                               //                |
    nop;                       //                |
    longjmp(buf, 2);           //  3---------------->|
    nop;                       //                |   |
                               //                |   |
  end;                         //                |   |
                               //                |   |
procedure func();              //  1<--------|   |   |
  begin                        //            |   |   |
    PORTB := 3;                //            |   |   |
    if (setjmp(buf) = 2) then  //  3<----------------|
      PORTB := 1               //  4-->|     |   |
    else                       //      |     |   |
      func33();                //  2------------>|
                               //      |     |
                               //  4<--|     |
  end;                         //  5----->|  |
                               //         |  |
begin                          //         |  |
    ADPCFG := 0xFFFF;          //         |  |
                               //         |  |
    PORTB := 0;                //         |  |
    TRISB := 0;                //         |  |
                               //         |  |
    nop;                       //         |  |
                               //         |  |
    func();                    //  1-------->|
                               //         |
    nop;                       //  5<-----|
    Delay_ms(1000);
    PORTB := 0xFFFF;
end.

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