I believe this is simply due to the 64 bits integer division. 1. Contrary to Java or most C implementations int is 64 bits with Go on AMD64, and not 32 bits. Integer division on 64 bits is more expensive than for 32 bits. 2. When array_length is known at compile time, the compiler can replace the integer division done for % with cheaper operations.
Regards, Didier. Le jeudi 25 mars 2021 à 20:02:52 UTC+1, Isaac Gouy a écrit : > ( > Yeah, it's a tiny tiny program from someone's language comparison > <http://www.hildstrom.com/projects/langcomp/index.html#:~:text=Results%20Table%20%20%20%20%20%20,%20%20225.9%20%2016%20more%20rows%20> > > but this is a hugely bigger slowdown than gcc or java? > > The code change is compile time constant — > array_length int = 100000000 > > — changed to run time value — > array_length int = 1000000 * iterations > ) > > > package main > import "os" > import "fmt" > import "strconv" > func main() { > var ( > element, iteration, iterations, innerloop int > sum float64 > ) > > if len(os.Args) > 1 { > iterations,_ = strconv.Atoi(os.Args[1]) > } > fmt.Printf("iterations %d\n", iterations) > > var ( > array_length int = 100000000 > array []float64 = make([]float64, array_length) > ) > > for element = 0; element < array_length; element++ { > array[element] = float64(element) > } > for iteration = 0; iteration < iterations; iteration++ { > for innerloop = 0; innerloop < 1000000000; innerloop++ { > sum += array[(iteration + innerloop) % array_length] > } > } > fmt.Printf("sum %E\n", sum) > array = nil > } > > $ /opt/src/go1.16/go/bin/go build -o out test.go > $ time ./out 100 > iterations 100 > sum 5.000000E+18 > > real 3m3.225s > > ==== > > package main > import "os" > import "fmt" > import "strconv" > func main() { > var ( > element, iteration, iterations, innerloop int > sum float64 > ) > > if len(os.Args) > 1 { > iterations,_ = strconv.Atoi(os.Args[1]) > } > fmt.Printf("iterations %d\n", iterations) > > var ( > array_length int = 1000000 * iterations > array []float64 = make([]float64, array_length) > ) > > for element = 0; element < array_length; element++ { > array[element] = float64(element) > } > for iteration = 0; iteration < iterations; iteration++ { > for innerloop = 0; innerloop < 1000000000; innerloop++ { > sum += array[(iteration + innerloop) % array_length] > } > } > fmt.Printf("sum %E\n", sum) > array = nil > } > > $ /opt/src/go1.16/go/bin/go build -o out test.go > $ time ./out 100 > iterations 100 > sum 5.000000E+18 > > real 18m20.737s > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/f235e967-1fb7-44d7-afa5-e0dd16d87798n%40googlegroups.com.
