Rust与Golang 的运算符优先级比较和除法与位运算的汇编比较

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Precedence    Operator
    5             *  /  %  <<  >>  &  &^
    4             +  -  |  ^
    3             ==  !=  <  <=  >  >=
    2             &&
    1             ||

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package main

func f1(left, right int) int {
	return (right - left) / 2
}

func f2(left, right int) int {
	return (right - left) >> 1
}

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// 指令长度: 18字节(下一行的size=18), 需要更多的指令来处理符号和溢出
main.f1 STEXT nosplit size=18 args=0x10 locals=0x0 funcid=0x0 align=0x0
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      TEXT    main.f1(SB), NOSPLIT|NOFRAME|ABIInternal, $0-16
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      FUNCDATA        $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      FUNCDATA        $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      FUNCDATA        $5, main.f1.arginfo1(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      FUNCDATA        $6, main.f1.argliveinfo(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:3)      PCDATA  $3, $1
        0x0000 00000 (G:/code/go/leetcode/array/main.go:4)      SUBQ    AX, BX          # BX = right - left
        0x0003 00003 (G:/code/go/leetcode/array/main.go:4)      MOVQ    BX, CX          # 备份差值到CX寄存器
        0x0006 00006 (G:/code/go/leetcode/array/main.go:4)      SHRQ    $63, BX         # 右移63位, 得到符号位(正数为0, 负数为-1)
        0x000a 00010 (G:/code/go/leetcode/array/main.go:4)      LEAQ    (CX)(BX*1), AX  # 修正偏移值
        0x000e 00014 (G:/code/go/leetcode/array/main.go:4)      SARQ    $1, AX          # 算数右移1位(等价于除以2)
        0x0011 00017 (G:/code/go/leetcode/array/main.go:4)      RET                     # 返回结果
        0x0000 48 29 c3 48 89 d9 48 c1 eb 3f 48 8d 04 19 48 d1  H).H..H..?H...H.
        0x0010 f8 c3
// 指令长度: 10字节(下一行的size=10)                                                    ..
main.f2 STEXT nosplit size=10 args=0x10 locals=0x0 funcid=0x0 align=0x0
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      TEXT    main.f2(SB), NOSPLIT|NOFRAME|ABIInternal, $0-16
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      FUNCDATA        $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      FUNCDATA        $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      FUNCDATA        $5, main.f2.arginfo1(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      FUNCDATA        $6, main.f2.argliveinfo(SB)
        0x0000 00000 (G:/code/go/leetcode/array/main.go:7)      PCDATA  $3, $1
        0x0000 00000 (G:/code/go/leetcode/array/main.go:8)      SUBQ    AX, BX           # BX = right - left
        0x0003 00003 (G:/code/go/leetcode/array/main.go:8)      SARQ    $1, BX           # 算数右移1位(等价于除以2)
        0x0006 00006 (G:/code/go/leetcode/array/main.go:8)      MOVQ    BX, AX           # 讲结果移动到返回寄存器AX
        0x0009 00009 (G:/code/go/leetcode/array/main.go:8)      RET                      # 返回结果
        0x0000 48 29 c3 48 d1 fb 48 89 d8 c3                    H).H..H...
go:cuinfo.producer.<unlinkable> SDWARFCUINFO dupok size=0
        0x0000 72 65 67 61 62 69                                regabi
go:cuinfo.packagename.main SDWARFCUINFO dupok size=0
        0x0000 6d 61 69 6e                                      main
main..inittask SNOPTRDATA size=8
        0x0000 00 00 00 00 00 00 00 00                          ........
gclocals·g2BeySu+wFnoycgXfElmcg== SRODATA dupok size=8
        0x0000 01 00 00 00 00 00 00 00                          ........
main.f1.arginfo1 SRODATA static dupok size=5
        0x0000 00 08 08 08 ff                                   .....
main.f1.argliveinfo SRODATA static dupok size=2
        0x0000 00 00                                            ..
main.f2.arginfo1 SRODATA static dupok size=5
        0x0000 00 08 08 08 ff                                   .....
main.f2.argliveinfo SRODATA static dupok size=2
        0x0000 00 00                                            ..                           ..

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#[unsafe(no_mangle)]
fn func1(left: i64, right: i64) -> i64 {
    (right - left) / 2
}

#[unsafe(no_mangle)]
fn func2(left: i64, right: i64) -> i64 {
    (right - left) >> 1
}

fn main() {

}

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	.globl	func1
	.p2align	4
func1:
	sub rdx, rcx     # 计算差值, rcx=left, rdx=right
	mov rax, rdx     # 将差值复制到rax寄存器, rax是64位返回值寄存器
	shr rax, 63      # 逻辑右移63位, 获得差值的符号位
	add rax, rdx     # 讲符号位加到原差值上, 实现负数除法时的向零取整修正
	sar rax, 1       # 算数右移1位(等价于除以2)
	ret

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	.globl	func2
	.p2align	4
func2:
	mov rax, rdx    # 将rdx的值复制到rax, rdx是第二个参数right
	sub rax, rcx    # rcx=left, 计算差值, rax = rac-rcx = right-left
	sar rax         # 算数右移1位(等价于除以2)
	ret				# 返回结果

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//go:noinline
func f3(left, right uint) uint {
	return (right - left) / 2
}

//go:noinline
func f4(left, right uint) uint {
	return (right - left) >> 1
}

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#[unsafe(no_mangle)]
fn func3(left: u64, right: u64) -> u64 {
    (left-right) >> 1
}


#[unsafe(no_mangle)]
fn func4(left: u64, right: u64) -> u64 {
    (left-right) / 2
}