From 1a5ff413c0cb96f14922fad905ce621d78859690 Mon Sep 17 00:00:00 2001
From: Bryce Kahle <bryce.kahle@datadoghq.com>
Date: Wed, 4 May 2022 10:19:17 +0000
Subject: [PATCH] internal: hard code endianness

This results in a reduction of the instructions necessary for endian-related operations.
The wall clock time difference for a single call is miniscule (picoseconds).

An example, with the ByteOrder.Uint32 function:
Runtime instructions: https://godbolt.org/z/7vW1Pfnso
Buildtime instructions: https://godbolt.org/z/baxW1Wb7W

The function call on amd64 changes from:

    MOVQ    "".NativeEndian(SB), CX
    MOVQ    "".NativeEndian+8(SB), DX
    MOVQ    64(CX), CX
    MOVQ    AX, BX
    MOVL    $4, DI
    MOVQ    DX, AX
    MOVQ    CX, DX
    MOVQ    DI, CX
    CALL    DX
to

    XCHGL   AX, AX

The difference on arm64 is equivalent, but uses different specific instructions.
---
 internal/endian.go    | 29 -----------------------------
 internal/endian_be.go | 13 +++++++++++++
 internal/endian_le.go | 13 +++++++++++++
 3 files changed, 26 insertions(+), 29 deletions(-)
 delete mode 100644 internal/endian.go
 create mode 100644 internal/endian_be.go
 create mode 100644 internal/endian_le.go

diff --git a/internal/endian.go b/internal/endian.go
deleted file mode 100644
index 6ae99fcd5..000000000
--- a/internal/endian.go
+++ /dev/null
@@ -1,29 +0,0 @@
-package internal
-
-import (
-	"encoding/binary"
-	"unsafe"
-)
-
-// NativeEndian is set to either binary.BigEndian or binary.LittleEndian,
-// depending on the host's endianness.
-var NativeEndian binary.ByteOrder
-
-// Clang is set to either "el" or "eb" depending on the host's endianness.
-var ClangEndian string
-
-func init() {
-	if isBigEndian() {
-		NativeEndian = binary.BigEndian
-		ClangEndian = "eb"
-	} else {
-		NativeEndian = binary.LittleEndian
-		ClangEndian = "el"
-	}
-}
-
-func isBigEndian() (ret bool) {
-	i := int(0x1)
-	bs := (*[int(unsafe.Sizeof(i))]byte)(unsafe.Pointer(&i))
-	return bs[0] == 0
-}
diff --git a/internal/endian_be.go b/internal/endian_be.go
new file mode 100644
index 000000000..ad33cda85
--- /dev/null
+++ b/internal/endian_be.go
@@ -0,0 +1,13 @@
+//go:build armbe || arm64be || mips || mips64 || mips64p32 || ppc64 || s390 || s390x || sparc || sparc64
+// +build armbe arm64be mips mips64 mips64p32 ppc64 s390 s390x sparc sparc64
+
+package internal
+
+import "encoding/binary"
+
+// NativeEndian is set to either binary.BigEndian or binary.LittleEndian,
+// depending on the host's endianness.
+var NativeEndian binary.ByteOrder = binary.BigEndian
+
+// ClangEndian is set to either "el" or "eb" depending on the host's endianness.
+const ClangEndian = "eb"
diff --git a/internal/endian_le.go b/internal/endian_le.go
new file mode 100644
index 000000000..41a68224c
--- /dev/null
+++ b/internal/endian_le.go
@@ -0,0 +1,13 @@
+//go:build 386 || amd64 || amd64p32 || arm || arm64 || mipsle || mips64le || mips64p32le || ppc64le || riscv64
+// +build 386 amd64 amd64p32 arm arm64 mipsle mips64le mips64p32le ppc64le riscv64
+
+package internal
+
+import "encoding/binary"
+
+// NativeEndian is set to either binary.BigEndian or binary.LittleEndian,
+// depending on the host's endianness.
+var NativeEndian binary.ByteOrder = binary.LittleEndian
+
+// ClangEndian is set to either "el" or "eb" depending on the host's endianness.
+const ClangEndian = "el"