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1brc's Issues

unit tests are not passing go 1.22 amd

the unit tests didn't pass for me on go 1.22amd. They are all failing heres the first two:

--- FAIL: TestMain (0.22s)
    --- FAIL: TestMain/test_cases\measurements-1 (0.02s)
       billionlinechallenge\main_test.go:18: 
            	Error Trace:	billionlinechallenge/main_test.go:18
            	Error:      	Not equal: 
            	            	expected: "{Kunming=19.8/19.8/19.8}\r\n"
            	            	actual  : "{Kunming=0.0/0.0/0.0}\n"
            	            	
            	            	Diff:
            	            	--- Expected
            	            	+++ Actual
            	            	@@ -1,2 +1,2 @@
            	            	-{Kunming=19.8/19.8/19.8}
            	            	+{Kunming=0.0/0.0/0.0}
            	            	 
            	Test:       	TestMain/test_cases\measurements-1
    --- FAIL: TestMain/test_cases\measurements-10 (0.01s)
       billionlinechallenge\main_test.go:18: 
            	Error Trace:	billionlinechallenge/main_test.go:18
            	Error:      	Not equal: 
            	            	expected: "{Adelaide=15.0/15.0/15.0, Cabo San Lucas=14.9/14.9/14.9, Dodoma=22.2/22.2/22.2, Halifax=12.9/12.9/12.9, Karachi=15.4/15.4/15.4, Pittsburgh=9.7/9.7/9.7, Ségou=25.7/25.7/25.7, Tauranga=38.2/38.2/38.2, Xi'an=24.2/24.2/24.2, Zagreb=12.2/12.2/12.2}\r\n"
            	            	actual  : "{Adelaide=0.0/0.0/0.0, Cabo San Lucas=0.0/0.0/0.0, Dodoma=0.0/0.0/0.0, Halifax=0.0/0.0/0.0, Karachi=0.0/0.0/0.0, Pittsburgh=84.5/84.5/84.5, Ségou=0.0/0.0/0.0, Tauranga=0.0/0.0/0.0, Xi'an=0.0/0.0/0.0, Zagreb=0.0/0.0/0.0}\n"
            	            	
            	            	Diff:
            	            	--- Expected
            	            	+++ Actual
            	            	@@ -1,2 +1,2 @@
            	            	-{Adelaide=15.0/15.0/15.0, Cabo San Lucas=14.9/14.9/14.9, Dodoma=22.2/22.2/22.2, Halifax=12.9/12.9/12.9, Karachi=15.4/15.4/15.4, Pittsburgh=9.7/9.7/9.7, Ségou=25.7/25.7/25.7, Tauranga=38.2/38.2/38.2, Xi'an=24.2/24.2/24.2, Zagreb=12.2/12.2/12.2}
            	            	+{Adelaide=0.0/0.0/0.0, Cabo San Lucas=0.0/0.0/0.0, Dodoma=0.0/0.0/0.0, Halifax=0.0/0.0/0.0, Karachi=0.0/0.0/0.0, Pittsburgh=84.5/84.5/84.5, Ségou=0.0/0.0/0.0, Tauranga=0.0/0.0/0.0, Xi'an=0.0/0.0/0.0, Zagreb=0.0/0.0/0.0}

Speed up `processReadChunk` by alternating bytes.IndexByte calls

I would not be surprised if you could speed up https://github.com/shraddhaag/1brc/blob/8513d5e70a1bfabbf46ab86a9cb6558bc9805154/main.go#L187C6-L187C22 by alternating calling bytes.IndexByte(buf[lastTokenEnd:], ';'), followed by bytes.IndexByte(buf[lastTokenEnd:], '\n'). bytes.IndexByte function is highly optimized for fast searching in a byte slice. Since it is the inner loop it can have a big impact.

You could probably also skip the looking at the first 1 byte for station name and temperature (since it's at least one character). From my experience not inspecting bytes can be a very efficient way of speeding up parsing.

Also, I would convert from []byte to string only when I need to to avoid any kind of unicode handling.

`customStringToIntParser` can likely be faster using a lookup table

I had a look at https://github.com/shraddhaag/1brc/blob/8513d5e70a1bfabbf46ab86a9cb6558bc9805154/main.go#L240C6-L240C29. Given that the temperatures are always within [-99.9, 99.9] and you know that it always has a tenth of accuracy, you can build up a string -> int lookup table on startup of your application. The lookup table will hold 1999 items. That way, parsing will be looking up the string in the lookup table. My gut feeling is this will be faster.

Caveat: I have not looked at the raw data file, nor have a ran the program.

Further read optimization

Hi, first of all thank you for sharing your code!

I was quite impressed by the reading speed, and I think that I found a way to make this part a bit faster:

1brc/main.go

Lines 131 to 155 in 8513d5e

// spawn a goroutine to read file in chunks and send it to the chunk channel for further processing
go func() {
buf := make([]byte, chunkSize)
leftover := make([]byte, 0, chunkSize)
for {
readTotal, err := file.Read(buf)
if err != nil {
if errors.Is(err, io.EOF) {
break
}
panic(err)
}
buf = buf[:readTotal]
toSend := make([]byte, readTotal)
copy(toSend, buf)
lastNewLineIndex := bytes.LastIndex(buf, []byte{'\n'})
toSend = append(leftover, buf[:lastNewLineIndex+1]...)
leftover = make([]byte, len(buf[lastNewLineIndex+1:]))
copy(leftover, buf[lastNewLineIndex+1:])
chunkStream <- toSend

Currently each loop calls 2 times make([]byte) and copy. This could be reduced to 1, by storing the leftover as a length, instead of a byte slice:

		buf := make([]byte, chunkSize)
		leftover := 0
		for {
			n, err := file.Read(buf[leftover:]) // append to the leftover
			if err != nil {
				if errors.Is(err, io.EOF) {
					break
				}
				panic(err)
			}
			toSend := buf[:leftover+n]

			lastNewLineIndex := bytes.LastIndexByte(toSend, '\n')

			buf = make([]byte, chunkSize) // prepare a new buffer for next read
			leftover = copy(buf, toSend[lastNewLineIndex+1:])

			chunkStream <- toSend[:lastNewLineIndex+1]
		}

On a sample file, this code is about 10% faster than the current version

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