From d481fa8dfe178c16f9ad89639715ddd7309f63f8 Mon Sep 17 00:00:00 2001
From: Wim Brand <wb@voclarion.nl>
Date: Thu, 17 May 2018 16:10:39 +0200
Subject: [PATCH] init

---
 main.go | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 main.go

diff --git a/main.go b/main.go
new file mode 100644
index 0000000..dc5fa88
--- /dev/null
+++ b/main.go
@@ -0,0 +1,111 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"os"
+	"runtime"
+	"sync"
+)
+
+const lf = byte('\n')
+
+func main() {
+	if len(os.Args) != 2 {
+		print("One argument required\n")
+		os.Exit(1)
+	}
+
+	f, err := os.Open("locate.txt")
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+
+	var needle = os.Args[1]
+
+	// To make sure all threads have ended when the program finishes
+	var wg sync.WaitGroup
+
+	// Make a channel and a thread for each CPU core
+	var cores = runtime.NumCPU()
+	var linechan = make(chan []byte)
+	for i := 0; i < cores; i++ {
+		go scannerThread(linechan, []byte(needle), &wg)
+		wg.Add(1)
+	}
+
+	var br = bufio.NewReaderSize(f, 1<<25) // reader with 32 MiB buffer
+	var buf = make([]byte, 1<<20)          // 1 MiB buffer for searching
+	var remainder []byte
+	var nread int
+
+	for {
+		nread, err = br.Read(buf)
+		if err != nil && err != io.EOF {
+			panic(err)
+		}
+		if err != io.EOF {
+			// Get the remainder of the last line
+			remainder, err = br.ReadBytes(byte('\n'))
+			if err != nil && err != io.EOF {
+				panic(err)
+			}
+		}
+
+		linechan <- append(buf[:nread], remainder...)
+
+		if err == io.EOF {
+			break
+		}
+	}
+
+	close(linechan)
+
+	wg.Wait()
+}
+
+func scannerThread(linechannel chan []byte, needle []byte, wg *sync.WaitGroup) {
+	var line []byte
+	var ok bool
+	var start, end int
+	var linelen int
+	var i int
+	defer wg.Done()
+	for {
+		line, ok = <-linechannel
+		if !ok {
+			return // channel closed. we're done
+		}
+
+		// This loop is for every result found, when there are no more results it stops
+		for i = bytes.Index(line, needle); i != -1; i = bytes.Index(line, needle) {
+			start, end = i, i
+			// needle was found, but where?
+			for { // find the start
+				if line[start] == lf {
+					start++ // the line feed is from the previous line, so skip it
+					break
+				} else if start == 0 {
+					break // result is at start of file
+				}
+				start--
+			}
+
+			for { // find the end
+				if line[end] == lf || end == linelen-1 {
+					break
+				}
+				end++
+			}
+
+			print(string(line[start:end]) + "\n")
+
+			// Chop all of the bytes before the result off so it doesn't get
+			// searched again
+			line = line[end:]
+			linelen = len(line)
+		}
+	}
+}