glisp/src/stack.c

#include "stack.h"

#include "memory.h"

#include <assert.h>

struct LispStack the_stack;

void lisp_init_stack() {
    the_stack.max_depth = DEFAULT_MAX_LISP_EVAL_DEPTH;
    the_stack.depth = 0;
    the_stack.first_clear_local_refs = 0;
    the_stack.frames =
        lisp_malloc(sizeof(struct StackFrame) * the_stack.max_depth);
    for (size_t i = 0; i < the_stack.max_depth; ++i) {
        the_stack.frames->local_refs.num_refs = 0;
        the_stack.frames->local_refs.num_blocks = 1;
        the_stack.frames->local_refs.blocks =
            lisp_malloc(sizeof(struct LocalReferencesBlock *));
        the_stack.frames->local_refs.blocks[0] =
            lisp_malloc(sizeof(struct LocalReferencesBlock));
    }
}

static ALWAYS_INLINE void init_stack_frame(struct StackFrame *frame,
                                           LispVal *name, LispVal *args) {
    frame->name = name;
    frame->args = args;
    frame->lexenv = Qnil;
}

void push_stack_frame(LispVal *name, LispVal *fobj, LispVal *args) {
    assert(the_stack.depth < the_stack.max_depth);
    struct StackFrame *frame = &the_stack.frames[the_stack.depth++];
    frame->name = name;
    frame->fobj = fobj;
    frame->args = args;
    frame->lexenv = Qnil;
}

static void reset_local_refs(struct LocalReferences *refs) {
    size_t last_block_size = refs->num_refs % LOCAL_REFERENCES_BLOCK_LENGTH;
    size_t num_full_blocks = refs->num_blocks / LOCAL_REFERENCES_BLOCK_LENGTH;
    for (size_t i = 0; i < num_full_blocks; ++i) {
        for (size_t j = 0; j < LOCAL_REFERENCES_BLOCK_LENGTH; ++j) {
            assert(OBJECTP(refs->blocks[i]->refs[j]));
            --((LispObject *) refs->blocks[i]->refs[j])->gc.local_ref_count;
        }
    }
    for (size_t i = 0; i < last_block_size; ++i) {
        assert(OBJECTP(refs->blocks[num_full_blocks]->refs[i]));
        --((LispObject *) refs->blocks[num_full_blocks]->refs[i])
              ->gc.local_ref_count;
    }
}

void pop_stack_frame(void) {
    assert(the_stack.depth > 0);
    struct StackFrame *frame = &the_stack.frames[--the_stack.depth];
    reset_local_refs(&frame->local_refs);
}

// return true if we allocated a block
static bool store_local_reference_in_frame(struct StackFrame *frame,
                                           LispVal *obj) {
    struct LocalReferences *refs = &frame->local_refs;
    size_t num_full_blocks = refs->num_refs / LOCAL_REFERENCES_BLOCK_LENGTH;
    if (num_full_blocks == refs->num_blocks) {
        refs->blocks =
            lisp_realloc(refs->blocks, sizeof(struct LocalReferencesBlock *)
                                           * ++refs->num_blocks);
        refs->blocks[refs->num_blocks - 1] =
            lisp_malloc(sizeof(struct LocalReferencesBlock));
        refs->blocks[refs->num_blocks - 1]->refs[0] = obj;
        refs->num_refs += 1;
        return true;
    } else {
        refs->blocks[num_full_blocks]
            ->refs[refs->num_refs++ % LOCAL_REFERENCES_BLOCK_LENGTH] = obj;
        return false;
    }
}

void add_local_reference(LispVal *obj) {
    assert(the_stack.depth > 0);
    if (OBJECTP(obj)) {
        if (store_local_reference_in_frame(LISP_STACK_TOP(), obj)) {
            the_stack.first_clear_local_refs = the_stack.depth;
        }
        ++((LispObject *) obj)->gc.local_ref_count;
    }
}