Texas Instruments TI89 Developer Guide - Page 1150

1108 Appendix A: System Routines - Utilities NeedStack Declaration: void NeedStack (short StackNeeded) Category(ies): Utilities Description: Throw an ER_MEMORY error if there is not at least StackNeeded bytes available on the hardware stack. The hardware stack is 16K in size. When a function calls another function the system will throw an ER_MEM_VIO error if there is not enough hardware stack to make the call. A function may have a complex set of operations that may not be easily undone in a ONERR block. The function may also require that all of the operations do not fail due to a lack of hardware stack. In this case, the function can be started with a call to NeedStack to at least guarantee that the hardware stack will not overflow during the critical section of the function. Inputs: StackNeeded - Minimum bytes of hardware stack required. Outputs: May throw an ER_MEMORY error. Assumptions: None Side Effects: None Availability: All versions of the TI-89 / TI-92 Plus. TI-89 / TI-92 Plus Differences: None See Also: None Example: The cmd_copyvar function has a TRY/ENDTRY block in case some of the operations it executes fail due to lack of heap memory (or because of locked variables and the like). But since it also directly modifies elements of the symbol table, it calls NeedStack first. The call to NeedStack insures that none of the critical operations are partially completed due to a lack of hardware stack thus leaving the symbol table in an undefined state. The TI-BASIC interpreter uses the hardware stack to make recursive calls and so all TI-BASIC commands and functions cannot rely on the hardware stack being at any particular level. NeedStack( 500 prepare to do copy . . . */ TRY /* . . . do copy . . . */ ONERR /* . . . recover from any known error conditions . . . */ ENDTRY TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001