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u3: adds jam variants to measure and encode in separate passes

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This commit is contained in:
Joe Bryan 2019-11-19 16:44:32 -08:00
parent b5312d6c0c
commit c166dff91c
2 changed files with 224 additions and 0 deletions
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13
pkg/urbit/include/noun/serial.h
View File

@ -11,3 +11,16 @@
*/
c3_w*
u3s_jam_fib(u3_noun a, c3_w* bit_w);
/* u3s_jam_met(): measure a noun for jam, calculating backrefs
*/
c3_d
u3s_jam_met(u3_noun a, u3p(u3h_root)* bak_p);
/* u3s_jam_buf(): jam [a] into [buf_w], without allocation
**
** using backrefs in [bak_p], as computed by u3s_jam_met
** can only encode up to c3_w bits
*/
void
u3s_jam_buf(u3_noun a, u3p(u3h_root) bak_p, c3_w* buf_w);

211
pkg/urbit/noun/serial.c
View File

@ -185,3 +185,214 @@ u3s_jam_fib(u3_noun a, c3_w* bit_w)
u3h_free(fib_u.har_p);
return fib_u.buf_w;
}
/* _cs_jam_met_mat(): the jam bitwidth of an atom of bitwidth [wid_w]
**
** equivalent to (head (rub a))
*/
static c3_d
_cs_jam_met_mat(c3_w wid_w)
{
return ( 0 == wid_w ) ? 1ULL :
(c3_d)wid_w + (2ULL * (c3_d)_cs_met0_w(wid_w));
}
/* _cs_jam_met: struct for tracking the jam bitwidth of a noun
*/
struct _cs_jam_met {
u3p(u3h_root) har_p;
u3p(u3h_root) bak_p;
c3_d len_d;
};
/* _cs_jam_met_atom_cb(): bitwidth of atom or backref encoding for [a]
*/
static void
_cs_jam_met_atom_cb(u3_atom a, void* ptr_v)
{
struct _cs_jam_met* met_u = ptr_v;
c3_w a_w = u3r_met(0, a);
u3_weak b = u3h_git(met_u->har_p, a);
// if we haven't haven't seen [a], put cursor into [har_p]
//
if ( u3_none == b ) {
u3h_put(met_u->har_p, a, u3i_chubs(1, &(met_u->len_d)));
met_u->len_d += 1ULL + _cs_jam_met_mat(a_w);
}
else {
c3_w b_w = u3r_met(0, b);
// if [a] is smaller than a backref, use directly
//
if ( a_w <= b_w ) {
met_u->len_d += 1ULL + _cs_jam_met_mat(a_w);
}
// otherwise, save backref
//
else {
u3h_put(met_u->bak_p, a, u3k(b));
met_u->len_d += 2ULL + _cs_jam_met_mat(b_w);
}
}
}
/* _cs_jam_met_cell_cb(): bitwidth of cell or backref encoding for [a]
*/
static c3_o
_cs_jam_met_cell_cb(u3_noun a, void* ptr_v)
{
struct _cs_jam_met* met_u = ptr_v;
u3_weak b = u3h_git(met_u->har_p, a);
// if we haven't haven't seen [a], put cursor into [har_p]
//
if ( u3_none == b ) {
u3h_put(met_u->har_p, a, u3i_chubs(1, &(met_u->len_d)));
met_u->len_d += 2ULL;
return c3y;
}
// otherwise, save backref and shortcircuit traversal
//
else {
c3_w b_w = u3r_met(0, b);
u3h_put(met_u->bak_p, a, u3k(b));
met_u->len_d += 2ULL + _cs_jam_met_mat(b_w);
return c3n;
}
}
/* u3s_jam_met(): measure a noun for jam, calculating backrefs
*/
c3_d
u3s_jam_met(u3_noun a, u3p(u3h_root)* bak_p)
{
struct _cs_jam_met met_u;
met_u.har_p = u3h_new();
met_u.bak_p = u3h_new();
met_u.len_d = 0ULL;
u3a_walk_fore(a, &met_u, _cs_jam_met_atom_cb,
_cs_jam_met_cell_cb);
u3h_free(met_u.har_p);
*bak_p = met_u.bak_p;
return met_u.len_d;
}
/* _cs_jam_buf: struct for tracking the pre-measured jam of a noun
*/
struct _cs_jam_buf {
u3p(u3h_root) bak_p;
c3_w bit_w;
c3_w* buf_w;
};
/* _cs_jam_buf_chop(): chop [met_w] bits of [a] into [buf_u]
*/
static void
_cs_jam_buf_chop(struct _cs_jam_buf* buf_u, c3_w met_w, u3_noun a)
{
u3r_chop(0, 0, met_w, buf_u->bit_w, buf_u->buf_w, a);
buf_u->bit_w += met_w;
}
/* _cs_jam_buf_mat(): length-prefixed encode (mat) [a] into [buf_u]
*/
static void
_cs_jam_buf_mat(struct _cs_jam_buf* buf_u, u3_atom a)
{
if ( 0 == a ) {
_cs_jam_buf_chop(buf_u, 1, 1);
}
else {
c3_w a_w = u3r_met(0, a);
c3_w b_w = _cs_met0_w(a_w);
_cs_jam_buf_chop(buf_u, b_w+1, 1 << b_w);
_cs_jam_buf_chop(buf_u, b_w-1, a_w & ((1 << (b_w-1)) - 1));
_cs_jam_buf_chop(buf_u, a_w, a);
}
}
/* _cs_jam_buf_atom_cb(): encode atom or backref
*/
static void
_cs_jam_buf_atom_cb(u3_atom a, void* ptr_v)
{
struct _cs_jam_buf* buf_u = ptr_v;
u3_weak b = u3h_git(buf_u->bak_p, a);
// if [a] has no backref (or this is the referent), encode atom
//
if ( (u3_none == b) ||
(u3r_word(0, b) == buf_u->bit_w) )
{
_cs_jam_buf_chop(buf_u, 1, 0);
_cs_jam_buf_mat(buf_u, a);
}
else {
c3_w a_w = u3r_met(0, a);
c3_w b_w = u3r_met(0, b);
// if [a] is smaller than the backref, encode atom
//
if ( a_w <= b_w ) {
_cs_jam_buf_chop(buf_u, 1, 0);
_cs_jam_buf_mat(buf_u, a);
}
// otherwise, encode backref
//
else {
_cs_jam_buf_chop(buf_u, 2, 3);
_cs_jam_buf_mat(buf_u, b);
}
}
}
/* _cs_jam_buf_cell_cb(): encode cell or backref
*/
static c3_o
_cs_jam_buf_cell_cb(u3_noun a, void* ptr_v)
{
struct _cs_jam_buf* buf_u = ptr_v;
u3_weak b = u3h_git(buf_u->bak_p, a);
// if [a] has no backref (or this is the referent), encode cell
//
if ( (u3_none == b) ||
(u3r_word(0, b) == buf_u->bit_w) )
{
_cs_jam_buf_chop(buf_u, 2, 1);
return c3y;
}
// otherwise, encode backref and shortcircuit traversal
//
else {
_cs_jam_buf_chop(buf_u, 2, 3);
_cs_jam_buf_mat(buf_u, b);
return c3n;
}
}
/* u3s_jam_buf(): jam [a] into pre-allocated [buf_w], without allocation
**
** using backrefs in [bak_p], as computed by u3s_jam_met()
** NB [buf_w] must be pre-allocated with sufficient space
**
** XX can only encode up to c3_w bits, due to use of chop
*/
void
u3s_jam_buf(u3_noun a, u3p(u3h_root) bak_p, c3_w* buf_w)
{
struct _cs_jam_buf buf_u;
buf_u.bak_p = bak_p;
buf_u.buf_w = buf_w;
buf_u.bit_w = 0;
// this is in fact safe under normal usage, as
// the stack will have been checked in u3s_jam_met()
//
u3a_walk_fore_unsafe(a, &buf_u, _cs_jam_buf_atom_cb,
_cs_jam_buf_cell_cb);
}