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If a pop operation on the stack causes the stack pointer to move past the origin of the stack, a stack underflow occurs. If a push operation causes the stack pointer to increment or decrement beyond the maximum extent of the stack, a stack overflow occurs. Some environments that rely heavily on stacks may provide additional operations, for example:
This stack grows downward from its origin. The stack pointer points to the current topmost datum on the stack. A push operation decrements the pointer and copies the data to the stack; a pop operation copies data from the stack and then increments the pointer. Each procedure called in the program stores procedure return information (in yellow ...
If frame pointers are being used, the prologue will typically set the new value of the frame pointer register from the stack pointer. Space on the stack for local variables can then be allocated by incrementally changing the stack pointer. The Forth programming language allows explicit winding of the call stack (called there the "return stack").
Typical examples of pointers are start pointers, end pointers, and stack pointers. These pointers can either be absolute (the actual physical address or a virtual address in virtual memory ) or relative (an offset from an absolute start address ("base") that typically uses fewer bits than a full address, but will usually require one additional ...
The programming languages Forth, Factor, RPL, PostScript, BibTeX style design language [2] and many assembly languages fit this paradigm. Stack-based algorithms manipulate data by popping data from and pushing data to the stack. Operators govern how the stack manipulates data. To emphasize the effect of a statement, a comment is often used ...
This uses operations to copy stack entries. The stack must be depth shallow enough for the CPU's available copy instructions. Hand-written stack code often uses this approach, and achieves speeds like general-purpose register machines. [30] [9] Unfortunately, algorithms for optimal "stack scheduling" are not in wide use by programming languages.
Scala normally manages the memory automatically in its JVM and JavaScript targets. However, the LLVM-based Scala Native compiler supports the use of pointers, as well as C-style heap allocation (e.g. malloc, realloc, free) and stack allocation (stackalloc). [22]
Unfortunately, in the middle of this operation, another thread may have done two pops and then pushed A back on top, resulting in the stack (A → C). The compare-and-swap succeeds in swapping `head` with `B`, and the result is that the stack now contains garbage (a pointer to the freed element "B").