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	sub function setjmp(dim byref env as word[4]) as 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	dim buf as word[4] ... Setjmp(buf)

Longjmp

Prototype	sub procedure longjmp(dim byref env as word[4], dim val as 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	dim buf as word[4] ... 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

dim buf as word[4]             ' Note: Program flow diagrams are indexed according
                               '       to the sequence of execution

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

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