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purego: add benchmarks for calling methods (#363)
Add benchmarks comparing SyscallN, RegisterFunc, and callback performance across different argument counts. This helps measure and compare the overhead of different calling approaches in purego's function invocation system. Closes #362
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‎syscall_bench_test.go‎

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// SPDX-License-Identifier: Apache-2.0
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// SPDX-FileCopyrightText: 2026 The Ebitengine Authors
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package purego_test
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import (
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"fmt"
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"os"
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"path/filepath"
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"testing"
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"github.com/ebitengine/purego"
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"github.com/ebitengine/purego/internal/load"
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)
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// BenchmarkCallingMethods compares RegisterFunc, SyscallN, and Callback methods
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func BenchmarkCallingMethods(b *testing.B) {
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testCases := []struct {
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n int
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goFn any
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goFnPtr uintptr
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cFnPtr uintptr
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cFnName string
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cCallbackPtr uintptr
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cCallbackName string
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args []int64
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expectedSum int64
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}{
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{1, goSum1, 0, 0, "sum1_c", 0, "call_callback1", []int64{1}, 1},
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{2, goSum2, 0, 0, "sum2_c", 0, "call_callback2", []int64{1, 2}, 3},
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{3, goSum3, 0, 0, "sum3_c", 0, "call_callback3", []int64{1, 2, 3}, 6},
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{5, goSum5, 0, 0, "sum5_c", 0, "call_callback5", []int64{1, 2, 3, 4, 5}, 15},
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{10, goSum10, 0, 0, "sum10_c", 0, "call_callback10", []int64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 55},
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{14, goSum15, 0, 0, "sum14_c", 0, "call_callback14", []int64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, 105},
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{15, goSum15, 0, 0, "sum15_c", 0, "call_callback15", []int64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}, 120},
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}
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// Build C library for benchmarking
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libFileName := filepath.Join(b.TempDir(), "libbenchmark.so")
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if err := buildSharedLib("CC", libFileName, filepath.Join("testdata", "benchmarktest", "benchmark.c")); err != nil {
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b.Fatalf("Failed to build C library: %v", err)
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}
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b.Cleanup(func() {
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os.Remove(libFileName)
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})
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libHandle, err := load.OpenLibrary(libFileName)
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if err != nil {
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b.Fatalf("Failed to load C library: %v", err)
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}
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b.Cleanup(func() {
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if err := load.CloseLibrary(libHandle); err != nil {
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b.Fatalf("Failed to close library: %s", err)
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}
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})
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// Create callbacks and load C functions
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for i := range testCases {
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testCases[i].goFnPtr = purego.NewCallback(testCases[i].goFn)
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cFn, err := load.OpenSymbol(libHandle, testCases[i].cFnName)
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if err != nil {
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b.Fatalf("Failed to load C function %s: %v", testCases[i].cFnName, err)
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}
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testCases[i].cFnPtr = cFn
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cCallbackFn, err := load.OpenSymbol(libHandle, testCases[i].cCallbackName)
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if err != nil {
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b.Fatalf("Failed to load C callback wrapper %s: %v", testCases[i].cCallbackName, err)
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}
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testCases[i].cCallbackPtr = cCallbackFn
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}
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b.Run("RegisterFunc/Callback", func(b *testing.B) {
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for _, tc := range testCases {
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b.Run(fmt.Sprintf("%dargs", tc.n), func(b *testing.B) {
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b.ReportAllocs()
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registerFn := makeRegisterFunc(tc.n)
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purego.RegisterFunc(registerFn, tc.goFnPtr)
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b.ResetTimer()
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result := callRegisterFunc(registerFn, tc.n, tc.args, b.N)
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b.StopTimer()
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if result != tc.expectedSum {
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b.Fatalf("RegisterFunc/Callback: expected sum %d, got %d", tc.expectedSum, result)
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}
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})
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}
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})
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// Benchmark RegisterFunc with C functions
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b.Run("RegisterFunc/CFunc", func(b *testing.B) {
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for _, tc := range testCases {
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b.Run(fmt.Sprintf("%dargs", tc.n), func(b *testing.B) {
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b.ReportAllocs()
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registerFn := makeRegisterFunc(tc.n)
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purego.RegisterFunc(registerFn, tc.cFnPtr)
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b.ResetTimer()
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result := callRegisterFunc(registerFn, tc.n, tc.args, b.N)
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b.StopTimer()
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if result != tc.expectedSum {
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b.Fatalf("RegisterFunc/CFunc: expected sum %d, got %d", tc.expectedSum, result)
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}
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})
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}
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})
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// Benchmark SyscallN with Go callbacks
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b.Run("SyscallN/Callback", func(b *testing.B) {
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for _, tc := range testCases {
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b.Run(fmt.Sprintf("%dargs", tc.n), func(b *testing.B) {
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b.ReportAllocs()
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args := int64sToUintptrs(tc.args)
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var result uintptr
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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result, _, _ = purego.SyscallN(tc.goFnPtr, args...)
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}
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b.StopTimer()
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if int64(result) != tc.expectedSum {
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b.Fatalf("SyscallN/Callback: expected sum %d, got %d", tc.expectedSum, result)
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}
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})
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}
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})
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// Benchmark SyscallN with C functions
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b.Run("SyscallN/CFunc", func(b *testing.B) {
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for _, tc := range testCases {
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b.Run(fmt.Sprintf("%dargs", tc.n), func(b *testing.B) {
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b.ReportAllocs()
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args := int64sToUintptrs(tc.args)
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var result uintptr
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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result, _, _ = purego.SyscallN(tc.cFnPtr, args...)
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}
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b.StopTimer()
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if int64(result) != tc.expectedSum {
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b.Fatalf("SyscallN/CFunc: expected sum %d, got %d", tc.expectedSum, result)
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}
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})
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}
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})
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// Benchmark round-trip: Go → C → Go callback (realistic use case)
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b.Run("RoundTrip/GoC", func(b *testing.B) {
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for _, tc := range testCases {
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b.Run(fmt.Sprintf("%dargs", tc.n), func(b *testing.B) {
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b.ReportAllocs()
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// Build args: first arg is callback pointer, rest are the arguments
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args := int64sToUintptrs(tc.args)
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callbackArgs := make([]uintptr, len(args)+1)
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callbackArgs[0] = tc.goFnPtr
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copy(callbackArgs[1:], args)
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// Skip if total args (callback + args) exceeds or meets limit
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// SyscallN has issues with exactly 15 or more arguments
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if len(callbackArgs) >= 15 {
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b.Skipf("Round-trip with %d args + callback (%d total) exceeds/meets SyscallN limit", tc.n, len(callbackArgs))
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}
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var result uintptr
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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result, _, _ = purego.SyscallN(tc.cCallbackPtr, callbackArgs...)
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}
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b.StopTimer()
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if int64(result) != tc.expectedSum {
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b.Fatalf("RoundTrip: expected sum %d, got %d", tc.expectedSum, result)
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}
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})
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}
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})
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}
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// makeRegisterFunc creates a function pointer of the appropriate signature
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func makeRegisterFunc(n int) any {
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switch n {
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case 1:
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return new(func(int64) int64)
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case 2:
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return new(func(int64, int64) int64)
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case 3:
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return new(func(int64, int64, int64) int64)
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case 5:
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return new(func(int64, int64, int64, int64, int64) int64)
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case 10:
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return new(func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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case 14:
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return new(func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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case 15:
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return new(func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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default:
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panic(fmt.Sprintf("unsupported arg count: %d", n))
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}
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}
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// callRegisterFunc calls the registered function with the appropriate number of arguments
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func callRegisterFunc(registerFn any, n int, args []int64, iterations int) int64 {
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var result int64
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switch n {
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case 1:
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f := registerFn.(*func(int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0])
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}
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case 2:
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f := registerFn.(*func(int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1])
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}
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case 3:
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f := registerFn.(*func(int64, int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1], args[2])
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}
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case 5:
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f := registerFn.(*func(int64, int64, int64, int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1], args[2], args[3], args[4])
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}
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case 10:
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f := registerFn.(*func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1], args[2], args[3], args[4],
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args[5], args[6], args[7], args[8], args[9])
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}
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case 14:
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f := registerFn.(*func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1], args[2], args[3], args[4],
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args[5], args[6], args[7], args[8], args[9],
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args[10], args[11], args[12], args[13])
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}
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case 15:
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f := registerFn.(*func(int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64, int64) int64)
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for i := 0; i < iterations; i++ {
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result = (*f)(args[0], args[1], args[2], args[3], args[4],
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args[5], args[6], args[7], args[8], args[9],
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args[10], args[11], args[12], args[13], args[14])
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}
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default:
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panic(fmt.Sprintf("unsupported arg count: %d", n))
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}
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return result
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}
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// int64sToUintptrs converts []int64 to []uintptr for SyscallN
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func int64sToUintptrs(args []int64) []uintptr {
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result := make([]uintptr, len(args))
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for i, v := range args {
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result[i] = uintptr(v)
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}
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return result
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}
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func goSum1(a1 int64) int64 { return a1 }
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func goSum2(a1, a2 int64) int64 { return a1 + a2 }
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func goSum3(a1, a2, a3 int64) int64 { return a1 + a2 + a3 }
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func goSum5(a1, a2, a3, a4, a5 int64) int64 { return a1 + a2 + a3 + a4 + a5 }
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func goSum10(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10 int64) int64 {
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return a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10
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}
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func goSum15(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 int64) int64 {
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return a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10 + a11 + a12 + a13 + a14 + a15
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}

‎testdata/benchmarktest/benchmark.c‎

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// SPDX-License-Identifier: Apache-2.0
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// SPDX-FileCopyrightText: 2026 The Ebitengine Authors
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#include <stdint.h>
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int64_t sum1_c(int64_t a1) { return a1; }
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int64_t sum2_c(int64_t a1, int64_t a2) { return a1 + a2; }
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int64_t sum3_c(int64_t a1, int64_t a2, int64_t a3) { return a1 + a2 + a3; }
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int64_t sum5_c(int64_t a1, int64_t a2, int64_t a3, int64_t a4, int64_t a5) {
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return a1 + a2 + a3 + a4 + a5;
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}
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int64_t sum10_c(int64_t a1, int64_t a2, int64_t a3, int64_t a4, int64_t a5,
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int64_t a6, int64_t a7, int64_t a8, int64_t a9, int64_t a10) {
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return a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10;
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}
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int64_t sum14_c(int64_t a1, int64_t a2, int64_t a3, int64_t a4, int64_t a5,
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int64_t a6, int64_t a7, int64_t a8, int64_t a9, int64_t a10,
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int64_t a11, int64_t a12, int64_t a13, int64_t a14) {
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return a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10 + a11 + a12 + a13 +
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a14;
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}
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int64_t sum15_c(int64_t a1, int64_t a2, int64_t a3, int64_t a4, int64_t a5,
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int64_t a6, int64_t a7, int64_t a8, int64_t a9, int64_t a10,
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int64_t a11, int64_t a12, int64_t a13, int64_t a14,
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int64_t a15) {
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return a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10 + a11 + a12 + a13 +
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a14 + a15;
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}
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typedef int64_t (*callback1_t)(int64_t);
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int64_t call_callback1(callback1_t cb, int64_t a1) { return cb(a1); }
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typedef int64_t (*callback2_t)(int64_t, int64_t);
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int64_t call_callback2(callback2_t cb, int64_t a1, int64_t a2) {
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return cb(a1, a2);
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}
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typedef int64_t (*callback3_t)(int64_t, int64_t, int64_t);
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int64_t call_callback3(callback3_t cb, int64_t a1, int64_t a2, int64_t a3) {
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return cb(a1, a2, a3);
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}
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typedef int64_t (*callback5_t)(int64_t, int64_t, int64_t, int64_t, int64_t);
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int64_t call_callback5(callback5_t cb, int64_t a1, int64_t a2, int64_t a3,
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int64_t a4, int64_t a5) {
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return cb(a1, a2, a3, a4, a5);
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}
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typedef int64_t (*callback10_t)(int64_t, int64_t, int64_t, int64_t, int64_t,
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int64_t, int64_t, int64_t, int64_t, int64_t);
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int64_t call_callback10(callback10_t cb, int64_t a1, int64_t a2, int64_t a3,
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int64_t a4, int64_t a5, int64_t a6, int64_t a7,
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int64_t a8, int64_t a9, int64_t a10) {
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return cb(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10);
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}
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typedef int64_t (*callback14_t)(int64_t, int64_t, int64_t, int64_t, int64_t,
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int64_t, int64_t, int64_t, int64_t, int64_t,
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int64_t, int64_t, int64_t, int64_t);
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int64_t call_callback14(callback14_t cb, int64_t a1, int64_t a2, int64_t a3,
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int64_t a4, int64_t a5, int64_t a6, int64_t a7,
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int64_t a8, int64_t a9, int64_t a10, int64_t a11,
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int64_t a12, int64_t a13, int64_t a14) {
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return cb(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14);
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}
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typedef int64_t (*callback15_t)(int64_t, int64_t, int64_t, int64_t, int64_t,
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int64_t, int64_t, int64_t, int64_t, int64_t,
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int64_t, int64_t, int64_t, int64_t, int64_t);
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int64_t call_callback15(callback15_t cb, int64_t a1, int64_t a2, int64_t a3,
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int64_t a4, int64_t a5, int64_t a6, int64_t a7,
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int64_t a8, int64_t a9, int64_t a10, int64_t a11,
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int64_t a12, int64_t a13, int64_t a14, int64_t a15) {
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return cb(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15);
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}

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