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bf: cond_stack -> loop_stack

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This commit is contained in:
Aryadev Chavali
2026-03-17 21:25:49 +00:00
parent 146921bdef
commit c6433b4429
1 changed files with 16 additions and 13 deletions
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29
src/bf.c
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@@ -19,22 +19,25 @@ void program_concat(struct ProgramConcat *ret, bf_token *a, bf_token *b)
memcpy(ret->tape + SIZEOF_PROGRAM, b, SIZEOF_PROGRAM);
}
// Represents the current execution context of the BrainFuck VM implementation.
// Used internally only, so its defined here.
struct MachineContext
{
u64 ip, head0, head1;
u64 total_iters;
};
// This function implements the jump-forward, given the current state of the
// machine. The main thing to concern us here is setting up the cond_stack
// correctly.
// This function implements the jump-forward operator of BrainFuck `[`, given
// the current state of the machine. We maintain a `loop_stack` which allows us
// to trivially implement the jump-back operator `]` - essentially heavy forward
// investment.
void loop_begin(struct ProgramConcat *prg, struct MachineContext *ctx,
vec_t *cond_stack)
vec_t *loop_stack)
{
// Add to cond_stack if not already present.
if (vec_find(cond_stack, &ctx->ip, sizeof(ctx->ip)) > cond_stack->size)
// Add to loop_stack if not already present.
if (vec_find(loop_stack, &ctx->ip, sizeof(ctx->ip)) > loop_stack->size)
{
vec_append(cond_stack, &ctx->ip, sizeof(ctx->ip));
vec_append(loop_stack, &ctx->ip, sizeof(ctx->ip));
}
// If tape at head0 is nonzero, then go to the next instruction.
@@ -74,8 +77,8 @@ void loop_begin(struct ProgramConcat *prg, struct MachineContext *ctx,
void program_execute(struct ProgramConcat *prg)
{
vec_t cond_stack = {0};
vec_ensure_capacity(&cond_stack, sizeof(prg->tape) * sizeof(u64));
vec_t loop_stack = {0};
vec_ensure_capacity(&loop_stack, sizeof(prg->tape) * sizeof(u64));
for (struct MachineContext ctx = {0};
ctx.ip < sizeof(prg->tape) && ctx.total_iters < (1LU << 13);
@@ -118,7 +121,7 @@ void program_execute(struct ProgramConcat *prg)
break;
case '[':
{
loop_begin(prg, &ctx, &cond_stack);
loop_begin(prg, &ctx, &loop_stack);
break;
}
case ']':
@@ -128,14 +131,14 @@ void program_execute(struct ProgramConcat *prg)
++ctx.ip;
continue;
}
else if (cond_stack.size < sizeof(u64))
else if (loop_stack.size < sizeof(u64))
{
// NOTE: as per paper, terminate.
ctx.ip = sizeof(prg->tape);
}
else
{
ctx.ip = *(u64 *)vec_pop(&cond_stack, sizeof(ctx.ip));
ctx.ip = *(u64 *)vec_pop(&loop_stack, sizeof(ctx.ip));
}
break;
}
@@ -145,7 +148,7 @@ void program_execute(struct ProgramConcat *prg)
}
}
vec_free(&cond_stack);
vec_free(&loop_stack);
}
void program_split(struct ProgramConcat *prg)