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u3: refactors +fein/+fynd jets and adds comments

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This commit is contained in:
Joe Bryan 2021-03-30 19:52:31 -07:00
parent 3b844532ba
commit 600c739a7a
2 changed files with 50 additions and 40 deletions
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40
pkg/urbit/jets/e/fein_ob.c
View File

@ -14,15 +14,16 @@ static const c3_w k_w = 0xffff0000;
//
static const c3_w rak_w[4] = { 0xb76d5eed, 0xee281300, 0x85bcae01, 0x4b387af7 };
/* _fe_ob(): +fe:ob, with constant parameters factored out.
** correct over the domain [0x0, 0xfffe.ffff]
*/
static c3_w
_feis_fe(c3_w m_w)
_fe_ob(c3_w m_w)
{
c3_w l_w = m_w % a_w;
c3_w r_w = m_w / a_w;
c3_w f_w, tmp_w;
c3_d tmp_d;
c3_y k_y[2];
c3_y j_y;
c3_w f_w, t_w;
c3_y j_y, k_y[2];
for ( j_y = 0; j_y < 4; j_y++ ) {
k_y[0] = r_w & 0xff;
@ -30,20 +31,28 @@ _feis_fe(c3_w m_w)
MurmurHash3_x86_32(k_y, 2, rak_w[j_y], &f_w);
tmp_d = (c3_d)f_w + l_w;
tmp_w = tmp_d % (!(j_y & 1) ? a_w: b_w);
// NB: this addition can overflow a c3_w (before mod)
//
t_w = ((c3_d)f_w + l_w) % (!(j_y & 1) ? a_w : b_w);
l_w = r_w;
r_w = tmp_w;
r_w = t_w;
}
return ( a_w == r_w ) ? (r_w * a_w) + l_w : (l_w * a_w) + r_w;
// legendary @max19
//
return ( a_w == r_w )
? (r_w * a_w) + l_w
: (l_w * a_w) + r_w;
}
/* _feis_ob(): +feis:ob, also offsetting by 0x1.000 (as in +fein:ob).
** correct over the domain [0x1.0000, 0xffff.ffff]
*/
static c3_w
_feis(c3_w m_w)
_feis_ob(c3_w m_w)
{
c3_w c_w = _feis_fe(m_w);
return ( c_w < k_w ) ? c_w : _feis_fe(c_w);
c3_w c_w = _fe_ob(m_w - b_w);
return b_w + (( c_w < k_w ) ? c_w : _fe_ob(c_w));
}
u3_atom
@ -56,10 +65,7 @@ u3qe_fein_ob(u3_atom pyn)
}
if ( 2 == sor_w ) {
c3_w pyn_w = u3r_word(0, pyn);
c3_w out_w = b_w + _feis(pyn_w - b_w);
return u3i_word(out_w);
return u3i_word(_feis_ob(u3r_word(0, pyn)));
}
else {
c3_w pyn_w[2];
@ -69,7 +75,7 @@ u3qe_fein_ob(u3_atom pyn)
return u3k(pyn);
}
else {
pyn_w[0] = b_w + _feis(pyn_w[0] - b_w);
pyn_w[0] = _feis_ob(pyn_w[0]);
return u3i_words(2, pyn_w);
}
}

44
pkg/urbit/jets/e/fynd_ob.c
View File

@ -10,46 +10,53 @@ static const c3_w a_w = 0xffff;
static const c3_w b_w = 0x10000;
static const c3_w k_w = 0xffff0000;
// +raku:ob
// (flop raku:ob)
//
static const c3_w rak_w[4] = { 0xb76d5eed, 0xee281300, 0x85bcae01, 0x4b387af7 };
static const c3_w kar_w[4] = { 0x4b387af7, 0x85bcae01, 0xee281300, 0xb76d5eed };
/* _fen_ob(): +fen:ob, with constant parameters factored out.
** correct over the domain [0x0 ... 0xfffe.ffff]
*/
static c3_w
_tail_fen(c3_w m_w)
_fen_ob(c3_w m_w)
{
c3_w l_w = m_w / a_w;
c3_w r_w = m_w % a_w;
c3_w f_w, tmp_w;
c3_y k_y[2];
c3_y j_y;
c3_w f_w, t_w;
c3_y j_y, k_y[2];
// legendary @max19
//
if ( a_w == l_w ) {
tmp_w = l_w;
t_w = l_w;
l_w = r_w;
r_w = tmp_w;
r_w = t_w;
}
for ( j_y = 4; j_y > 0; j_y-- ) {
for ( j_y = 0; j_y < 4; j_y++ ) {
k_y[0] = l_w & 0xff;
k_y[1] = (l_w >> 8) & 0xff;
MurmurHash3_x86_32(k_y, 2, rak_w[j_y - 1], &f_w);
MurmurHash3_x86_32(k_y, 2, kar_w[j_y], &f_w);
tmp_w = ( j_y & 1 )
t_w = ( j_y & 1 )
? ((r_w + a_w) - (f_w % a_w)) % a_w
: ((r_w + b_w) - (f_w % b_w)) % b_w;
r_w = l_w;
l_w = tmp_w;
l_w = t_w;
}
return (r_w * a_w) + l_w;
}
/* _tail_ob(): +feis:ob, also offsetting by 0x1.000 (as in +fynd:ob).
** correct over the domain [0x1.0000, 0xffff.ffff]
*/
static c3_w
_tail(c3_w m_w)
_tail_ob(c3_w m_w)
{
c3_w c_w = _tail_fen(m_w);
return ( c_w < k_w ) ? c_w : _tail_fen(c_w);
c3_w c_w = _fen_ob(m_w - b_w);
return b_w + (( c_w < k_w ) ? c_w : _fen_ob(c_w));
}
u3_atom
@ -62,10 +69,7 @@ u3qe_fynd_ob(u3_atom pyn)
}
if ( 2 == sor_w ) {
c3_w pyn_w = u3r_word(0, pyn);
c3_w out_w = b_w + _tail(pyn_w - b_w);
return u3i_word(out_w);
return u3i_word(_tail_ob(u3r_word(0, pyn)));
}
else {
c3_w pyn_w[2];
@ -75,7 +79,7 @@ u3qe_fynd_ob(u3_atom pyn)
return u3k(pyn);
}
else {
pyn_w[0] = b_w + _tail(pyn_w[0] - b_w);
pyn_w[0] = _tail_ob(pyn_w[0]);
return u3i_words(2, pyn_w);
}
}