rajamesandClaude Opus 5.5
0da7e32a0b
Ruled 2026-10-04, revising D-2: stack overflow and underflow are errors that are shown and return to the prompt, not silent wrap-around. - Each stack counts what it holds. Before every opcode the executor checks that the stacks hold what it takes and have room for what it leaves; otherwise the opcode does nothing and the node faults, as for a bad address, to that kind's handler. Every fault empties both stacks. - The fault handler is now a table of five jumps: address, data overflow, data underflow, return overflow, return underflow. The host node says "Stack overflow", "Stack underflow", "Return stack overflow", "Return stack underflow", then ERROR and the prompt. - Two registers, DSTACK-DEPTH and RSTACK-DEPTH: a fetch reads the depth, a store empties the stack. QUIT, ABORT and the error exits empty the return stack before they call anything; ABORT empties the data stack. - capsule/forth.v4: DEPTH, PICK and ROLL, to FORTH-79 (counting from one). PICK and ROLL set the values above the one wanted aside in memory, and work with the stack full. - Division by zero now takes its operands off the stack, as v3 does. - A colon with no room for its entry abandons the line. - tests: every opcode at every depth of both stacks; the faults, the registers and the three words from the prompt. The sizes are unchanged: ten values, nine return entries. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
65 lines
2.9 KiB
C
65 lines
2.9 KiB
C
/* exec.h -- instruction execution for v4.
|
|
*
|
|
* DECOMPOSITION.md section 1.2: "Slots execute left to right." A branch
|
|
* (jump, call, next, if, -if) takes its target from all bits to the right of
|
|
* its slot and replaces the same low bits of P (page-relative). Branches are
|
|
* legal in slots 0-3 only. Nothing to the right of a branch executes, taken
|
|
* or not, because those bits are its address.
|
|
*
|
|
* Section 1.4: "Every retired instruction increments that opcode's heat counter
|
|
* and advances the anti-clock; every `call` increments the heat counter of its
|
|
* target. None of this costs an instruction."
|
|
*
|
|
* The node owns P, A, B, the stacks and memory; heat and the anti-clock are
|
|
* separate physics state (section 7 names them as registers).
|
|
*
|
|
* THREE POINTS THE SPEC LEAVES TO THE F18, and which this model takes from it:
|
|
*
|
|
* - `ex` ends the word, like `;`. P has been replaced, so the remaining
|
|
* slots belong to a word that is no longer the current one.
|
|
* - `unext` restarts the *already fetched* word at slot 0. It does not
|
|
* refetch and does not move P, so `@p` and `!p` inside a unext loop step
|
|
* through the words that follow the loop word. When R reaches 0 the loop
|
|
* ends and execution continues with the slot after `unext`.
|
|
* - `+*` shifts T arithmetically (sign bit kept). Section 1.3 says only
|
|
* "shift T:A right one bit"; D-3 says plain F18 semantics.
|
|
*
|
|
* A branch opcode in slot 4 or 5 is outside the spec. The model does not trap
|
|
* it: it applies the 7- or 2-bit target the layout formula gives.
|
|
*/
|
|
#ifndef V4_EXEC_H
|
|
#define V4_EXEC_H
|
|
|
|
#include "v4/heat.h"
|
|
#include "v4/iword.h"
|
|
#include "v4/node.h"
|
|
|
|
typedef struct {
|
|
v4_uheat_t anticlock;
|
|
} v4_exec_state;
|
|
|
|
void v4_exec_reset(v4_exec_state *es);
|
|
|
|
/* Execute one instruction word: fetch at P, advance P, run the slots left to
|
|
* right until the word ends. A unext loop runs to completion inside one call,
|
|
* so the call does not return while R is nonzero at a `unext`. Returns the
|
|
* number of instructions retired.
|
|
*
|
|
* FAULTS (node.h; D-14 and D-16). Before an opcode runs, the stacks must
|
|
* hold what it takes -- a T or S it only reads counts -- and have room for
|
|
* what it leaves; and an address it uses, or P at the fetch, must be inside
|
|
* node memory. If not, that opcode and the rest of the word do not execute,
|
|
* both stacks are emptied, and P is that kind's word of the node's fault
|
|
* table on return. With no table the node stops, and this does nothing and
|
|
* returns 0 from then on. */
|
|
unsigned v4_exec_step_word(v4_node *n, v4_exec_state *es, v4_heat *h);
|
|
|
|
/* Execute a single opcode. The branch opcodes read their target from `w` and
|
|
* `slot`; every other opcode ignores both. `unext` here only updates R; the
|
|
* restart is v4_exec_step_word's. A value above 31 does nothing and retires
|
|
* nothing. */
|
|
void v4_exec_op(v4_node *n, v4_exec_state *es, v4_heat *h,
|
|
unsigned op, v4_iword w, unsigned slot);
|
|
|
|
#endif /* V4_EXEC_H */
|