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Initial pass at the 1BRC
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package main | |
import ( | |
"bytes" | |
"errors" | |
"flag" | |
"io" | |
"log" | |
"os" | |
"sort" | |
"sync" | |
) | |
type row struct { | |
name string | |
sum int64 | |
count uint32 | |
min int16 | |
max int16 | |
} | |
func (r *row) appendLen() int { return len(r.name) + len("=-00.0/-00.0/-00.0, ") } | |
func (r *row) append(b []byte) []byte { | |
b = append(b, r.name...) | |
b = append(b, '=') | |
b = appendFixedFloat(b, r.min) | |
b = append(b, '/') | |
b = appendFixedFloat(b, r.sum/int64(r.count)) | |
b = append(b, '/') | |
b = appendFixedFloat(b, r.max) | |
return append(b, ',', ' ') | |
} | |
func appendFixedFloat[T int16 | int64](p []byte, i T) []byte { | |
if i < 0 { | |
p = append(p, '-') | |
i = -i | |
} | |
if i <= 9 { | |
return append(p, '0', '.', byte(i)+'0') | |
} | |
j := i / 10 | |
if j <= 9 { | |
return append(p, byte(j)+'0', '.', byte(i-j*10)+'0') | |
} | |
k := j / 10 | |
return append(p, byte(k)+'0', byte(j-k*10)+'0', '.', byte(i-j*10+'0')) | |
} | |
func main() { | |
var name string | |
fs := flag.NewFlagSet(os.Args[0], flag.ExitOnError) | |
fs.StringVar(&name, "input", "/data/measurements.txt", "file to load") | |
if err := fs.Parse(os.Args[1:]); err != nil { | |
panic("unreachable") | |
} | |
s, err := processFile(name) | |
if err != nil { | |
log.Fatalf("failed to process %q: %v", name, err) | |
} | |
s.writeResults(os.Stdout) | |
} | |
func processFile(name string) (stats, error) { | |
f, err := os.Open(name) | |
if err != nil { | |
return nil, err | |
} | |
defer f.Close() | |
return processReader(f, 4*1024*1024, 4) | |
} | |
func processReader(r io.Reader, chunkSize, workerCount int) (stats, error) { | |
var wg sync.WaitGroup | |
workCh := make(chan []byte, workerCount) | |
freeCh := make(chan []byte, 1+workerCount) | |
statsCh := make(chan stats, workerCount) | |
for range workerCount { | |
wg.Add(1) | |
go func() { | |
defer wg.Done() | |
freeCh <- make([]byte, chunkSize) | |
s := make(stats, 1<<10) | |
for lines := range workCh { | |
s.processLines(lines) | |
freeCh <- lines | |
} | |
statsCh <- s | |
}() | |
} | |
buf := make([]byte, chunkSize) | |
n, err := r.Read(buf) | |
for n > 0 { | |
lines, broken := cutAfterLast(buf[:n], '\n') | |
buf = <-freeCh | |
buf = append(buf[:0], broken...) | |
workCh <- lines | |
n, err = r.Read(buf[len(buf):cap(buf)]) | |
n += len(buf) | |
} | |
close(workCh) | |
wg.Wait() | |
close(freeCh) | |
close(statsCh) | |
if err != nil { | |
if !errors.Is(err, io.EOF) { | |
return nil, err | |
} | |
err = nil | |
} | |
s := <-statsCh | |
for m := range statsCh { | |
for name, row := range m { | |
if r, ok := s[name]; ok { | |
r.sum += row.sum | |
r.count += row.count | |
r.min = min(r.min, row.min) | |
r.max = max(r.max, row.max) | |
continue | |
} | |
s[name] = row | |
} | |
} | |
return s, err | |
} | |
type stats map[string]*row | |
func (s stats) processLines(lines []byte) { | |
var city, value []byte | |
var rows []row | |
for len(lines) > 0 { | |
city, lines = cut(lines, ';') | |
value, lines = cut(lines, '\n') | |
t := parseTemp(value) | |
if r, ok := s[string(city)]; ok { | |
r.sum += int64(t) | |
r.count++ | |
r.min = min(r.min, t) | |
r.max = max(r.max, t) | |
continue | |
} | |
if len(rows) == 0 { | |
rows = make([]row, 64) | |
} | |
r := &rows[0] | |
rows = rows[1:] | |
r.name = string(city) | |
r.sum = int64(t) | |
r.count = 1 | |
r.min = t | |
r.max = t | |
s[r.name] = r | |
} | |
} | |
func (s stats) writeResults(w io.Writer) error { | |
ordered := make([]*row, len(s)) | |
i := 0 | |
for _, r := range s { | |
ordered[i] = r | |
i++ | |
} | |
sort.Slice(ordered, func(i, j int) bool { return ordered[i].name < ordered[j].name }) | |
b := make([]byte, 0, 8<<10) | |
b = append(b, '{') | |
for _, r := range ordered { | |
if r.appendLen() > cap(b)-len(b) { | |
// Flush | |
n, err := w.Write(b) | |
if err != nil { | |
return err | |
} | |
b = append(b[:0], b[n:]...) | |
} | |
b = r.append(b) | |
} | |
b = append(b, '}', '\n') | |
_, err := w.Write(b) | |
return err | |
} | |
func parseTemp(b []byte) int16 { | |
if len(b) == 0 { | |
return 0 | |
} | |
if b[0] == '-' { | |
return -parseNonNegative(b[1:]) | |
} | |
return parseNonNegative(b) | |
} | |
func parseNonNegative(b []byte) int16 { | |
var i, x int | |
for ; i < len(b) && b[i]-'0' <= 9; i++ { | |
x += int(b[i] - '0') | |
x *= 10 | |
} | |
if i < len(b) { | |
b = b[i:] | |
if len(b) >= 2 && b[0] == '.' { | |
if d := b[1] - '0'; d <= 9 { | |
x += int(d) | |
} | |
} | |
} | |
return int16(x) | |
} | |
func cut(s []byte, c byte) (prefix []byte, suffix []byte) { | |
if i := bytes.IndexByte(s, c); i >= 0 { | |
return s[:i], s[i+1:] | |
} | |
return s, nil | |
} | |
// cutAfterLast returns s split into two, after the last location of byte c | |
func cutAfterLast(b []byte, c byte) ([]byte, []byte) { | |
if i := bytes.LastIndexByte(b, c); i >= 0 { | |
i++ | |
return b[:i], b[i:] | |
} | |
return nil, b | |
} |
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