Run-based 1-byte /⁼ implementation

This commit is contained in:
Marshall Lochbaum 2024-04-29 21:04:27 -04:00
parent 092ba4167a
commit e681f3c09a
2 changed files with 65 additions and 20 deletions

View File

@ -28,36 +28,31 @@ fn count{T}(tab:*usz, x:*T, n:u64, min_allowed:T) : T = {
r0:u64 = 0 # Elements actually handled by vector case
# Find range to check for suitability; return a negative if found
# Also record number of differences dc
# (double-counts at index vec but it doesn't need to be exact)
xv := *V~~x
jv := load{xv}; mv := jv
@for (xv over _ from 1 to b) { jv = min{jv, xv}; mv = max{mv, xv} }
jv := load{xv}; mv := jv; dc := -(jv != load{*V~~(x+1)})
@for (xv, xp in *V~~(x-1) over _ from 1 to b) {
jv = min{jv, xv}; mv = max{mv, xv}
dc -= xp != xv
}
@for (x over _ from rv to r) { if (x<min_allowed) return{x}; if (x>mx) mx=x }
jt := vfold{min, jv}
mt := vfold{max, mv}
if (jt < min_allowed) return{jt}
if (mt > mx) mx = mt
# Fast cases
dt := promote{u64, fold_addw{dc}}
nc := uT~~(mt - jt) # Number of counts to perform: last is implicit
if (nc <= 24*vbits/128) {
if (dt < b * (vec/2) and dt*8 < b * promote{u64,nc}) {
r0 = count_with_runs{V, vec, x, tab, r}
} else if (nc <= 24*vbits/128) {
r0 = rv
j0 := promote{u64, uT~~jt} # Starting count
m := promote{u64, nc} # Number of iterations
total := trunc{usz, r0} # To compute last count
def count_each{js, num} = {
j := @collect (k to num) trunc{T, js+k}
c := copy{length{j}, [vec]uT ** 0}
e := each{{j}=>V**j, j}
@for (xv over b) each{{c,e} => c -= xv == e, c, e}
def add_sum{c, j} = {
s := promote{usz, fold_addw{c}}
total -= s; inc{tab, j, s}
}
each{add_sum, c, j}
count_by_sum{T, V, [vec]uT, xv, b, tab, r0,
promote{u64, uT~~jt}, # Starting count
promote{u64, nc} # Number of iterations
}
m4 := m / 4
@for (j4 to m4) count_each{j0 + 4*j4, 4}
@for (j from 4*m4 to m) count_each{j0 + j, 1}
inc{tab, trunc{T, j0 + m}, trunc{usz,total}}
}
# Scalar fallback and cleanup
@ -68,4 +63,52 @@ fn count{T}(tab:*usz, x:*T, n:u64, min_allowed:T) : T = {
mx
}
# Sum comparisons against each value (except one) in the range
def count_by_sum{T, V, U, xv, b, tab, r0, j0, m} = {
total := trunc{usz, r0} # To compute last count
def count_each{js, num} = {
j := @collect (k to num) trunc{T, js+k}
c := copy{length{j}, U**0}
e := each{{j}=>V**j, j}
@for (xv over b) each{{c,e} => c -= xv == e, c, e}
def add_sum{c, j} = {
s := promote{usz, fold_addw{c}}
total -= s; inc{tab, j, s}
}
each{add_sum, c, j}
}
m4 := m / 4
@for (j4 to m4) count_each{j0 + 4*j4, 4}
@for (j from 4*m4 to m) count_each{j0 + j, 1}
inc{tab, trunc{T, j0 + m}, trunc{usz,total}}
}
# Count adjacent equal elements at once, breaking at w-element groups
# May read up to index r from x, hitting one element that's not counted
def count_with_runs{V, vec, x, tab, r} = {
def w = width{ux}
m0:ux = 1 << (w-1) # Last element in each chunk ends a run
bw := r / w
@for (i to bw) {
xo := x + i*w
m := m0
# Mark the end of each run
@unroll (j to w / vec) {
def jv = j*vec
def lv{k} = load{*V~~(xo + k)}
m |= promote{ux, homMask{lv{jv} != lv{jv+1}}} << jv
}
# Iterate over runs
jp:usz = - usz~~1
while (m > m0) @unroll (2) {
j := trunc{usz, ctz{m}}
inc{tab, load{xo, j}, j - jp}
jp = j; m &= m-1
}
# One step if popc{m} was odd, reducing branch mispredictions above
inc{tab, load{xo, w-1}, ((w-1) - jp) & -trunc{usz, m>>(w-1)}}
}
bw * w
}
export{'avx2_count_i8', count{i8}}

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@ -15,6 +15,8 @@ def ntyp{S, ...S2, T if w128{T}} = merge{S, 'q', ...S2, '_', nty{T}}
def ntyp{S, ...S2, T if w64{T}} = merge{S, ...S2, '_', nty{T}}
def ntyp0{S, T} = merge{S, '_', nty{T}}
def __neg{a:T if nvecu{T}} = T~~(-ty_s{T}~~a)
def __lt{a:T, 0 if nvecs{T} or nvecf{T}} = emit{ty_u{T}, ntyp{'vcltz', T}, a}
def __le{a:T, 0 if nvecs{T} or nvecf{T}} = emit{ty_u{T}, ntyp{'vclez', T}, a}
def __gt{a:T, 0 if nvecs{T} or nvecf{T}} = emit{ty_u{T}, ntyp{'vcgtz', T}, a}