sandbox/doc/part-0x07.rst

126 lines
3.2 KiB
ReStructuredText
Raw Normal View History

Write You a Forth, 0x07
-----------------------
:date: 2018-03-01 19:31
:tags: wyaf, forth
2018-03-02 04:04:34 +00:00
At this point, I've finished most of the nucleus layer. All that's left to
implement are ``EXIT``, ``I``, and ``J`` --- the first requires better
execution support, which I'll talk about at the end. The other two, I'm not so
sure about yet.
However, I made some large changes, so let's dive in. Here's the new Linux
definitions file::
#ifndef __KF_LINUX_DEFS_H__
#define __KF_LINUX_DEFS_H__
#include <stddef.h>
#include <stdint.h>
typedef int32_t KF_INT;
typedef uint32_t KF_UINT;
typedef int64_t KF_LONG;
typedef uintptr_t KF_ADDR;
constexpr uint8_t STACK_SIZE = 128;
constexpr size_t ARENA_SIZE = 65535;
#endif
I've also updated the main ``defs.h`` file to move some constants there::
#ifndef __KF_DEFS_H__
#define __KF_DEFS_H__
#ifdef __linux__
#include "linux/defs.h"
#else
typedef int KF_INT;
typedef long KF_LONG;
constexpr uint8_t STACK_SIZE = 16;
#endif
constexpr size_t MAX_TOKEN_LENGTH = 16;
constexpr size_t dshift = (sizeof(KF_INT) * 8) - 1;
static inline KF_INT
mask(size_t bits)
{
KF_INT m = 0;
for (size_t i = 0; i < bits; i++) {
m += 1 << i;
}
return m;
}
#endif // __KF_DEFS_H__
Addresses
^^^^^^^^^
The first major change is the addition of the ``KF_ADDR`` type. This is needed
to implement the memory manipulation words. I've added some additional utility
functions for pushing and popping addresses from the data stack; they're stored
as double numbers::
static bool
pop_addr(System *sys, KF_ADDR *a)
{
KF_LONG b;
if (!pop_long(sys, &b)) {
// Status is already set.
return false;
}
*a = static_cast<KF_ADDR>(b);
sys->status = STATUS_OK;
return true;
}
static bool
push_addr(System *sys, KF_ADDR a)
{
KF_LONG b = static_cast<KF_LONG>(a);
if (!push_long(sys, b)) {
// Status is already set.
return false;
}
sys->status = STATUS_OK;
return true;
}
Now I can actually implement ``!`` and so forth::
static bool
store(System *sys)
{
KF_ADDR a = 0; // address
KF_INT b = 0; // value
KF_LONG c = 0; // temporary
if (!pop_long(sys, &c)) {
sys->status = STATUS_STACK_UNDERFLOW;
return false;
}
a = static_cast<KF_ADDR>(c);
if (!sys->dstack.pop(&b)) {
sys->status = STATUS_STACK_UNDERFLOW;
return false;
}
*((KF_INT *)a) = b;
sys->status = STATUS_OK;
return true;
}
There's definitely a sense of finangling here.
The return stack
^^^^^^^^^^^^^^^^
The ``>R`` series of words requires a