測試while(u--);和while(u)u--;的區別
阿新 • • 發佈：2019-02-13
測試結果居然效率二者不一樣。u=500;while(u--);慢一些。執行一次用時2300ns。後者快一些，1900ns。
測試方法：連續執行100000次，統計平均時間。
cpu: intel core2 4300 1.8GHz
OS: x86_64-suse-linux
使用GCC。版本：4.5.0 20100604.
以下是程式碼。
#include <gtk/gtk.h>
int main(int argc,char **argv)
{
//make some test...and Ajust the param
if(1)
{
GTimeVal tStart,tEnd;
g_get_current_time(&tStart);
gchar str[100] = "while(u--)";
gint loops = 100000;
gint u_org = 500;
gint loops_cpy = loops;
while(loops_cpy--)
{
gint u = u_org;//stop and have a rest before each packet
while(u--);
}
g_get_current_time(&tEnd);
gfloat time_msec = (1000000.00*(tEnd.tv_sec - tStart.tv_sec)+ tEnd.tv_usec-tStart.tv_usec)/1000;
gfloat time_each = time_msec / loops * 1000000;
g_print("Time %s: %.2fms used for %d loops. Each loop %.2fns\n",str,time_msec,loops,time_each);
}
if(1)
{
GTimeVal tStart,tEnd;
g_get_current_time(&tStart);
gchar str[100] = "while(u)u--";
gint loops = 100000;
gint u_org = 500;
gint loops_cpy = loops;
while(loops_cpy--)
{
gint u = u_org;//stop and have a rest before each packet
while(u)u--;
}
g_get_current_time(&tEnd);
gfloat time_msec = (1000000.00*(tEnd.tv_sec - tStart.tv_sec)+ tEnd.tv_usec-tStart.tv_usec)/1000;
gfloat time_each = time_msec / loops * 1000000;
g_print("Time %s: %.2fms used for %d loops. Each loop %.2fns\n",str,time_msec,loops,time_each);
}
return 0;
}
彙編程式碼：
.file "a.c" .section .debug_abbrev,"",@progbits .Ldebug_abbrev0: .section .debug_info,"",@progbits .Ldebug_info0: .section .debug_line,"",@progbits .Ldebug_line0: .text .Ltext0: .section .rodata .align 8 .LC3: .string "Time %s: %.2fms used for %d loops. Each loop %.2fns\n" .text .globl main .type main, @function main: .LFB9: .file 1 "a.c" .loc 1 6 0 .cfi_startproc pushq %rbp .LCFI0: .cfi_def_cfa_offset 16 movq %rsp, %rbp .cfi_offset 6, -16 .LCFI1: .cfi_def_cfa_register 6 subq $240, %rsp movl %edi, -228(%rbp) movq %rsi, -240(%rbp) .LBB2: .loc 1 11 0 leaq -64(%rbp), %rax movq %rax, %rdi call g_get_current_time .loc 1 12 0 movl $1818847351, -224(%rbp) movl $762652773, -220(%rbp) movq $10541, -216(%rbp) leaq -208(%rbp), %rdx movl $0, %eax movl $10, %ecx movq %rdx, %rdi rep stosq movq %rdi, %rdx movl %eax, (%rdx) addq $4, %rdx .loc 1 13 0 movl $100000, -20(%rbp) .loc 1 14 0 movl $500, -24(%rbp) .loc 1 15 0 movl -20(%rbp), %eax movl %eax, -4(%rbp) .loc 1 16 0 jmp .L2 .L4: .LBB3: .loc 1 18 0 movl -24(%rbp), %eax movl %eax, -8(%rbp) .loc 1 19 0 nop .L3: .loc 1 19 0 is_stmt 0 discriminator 1 cmpl $0, -8(%rbp) setne %al subl $1, -8(%rbp) testb %al, %al jne .L3 .L2: .LBE3: .loc 1 16 0 is_stmt 1 discriminator 1 cmpl $0, -4(%rbp) setne %al subl $1, -4(%rbp) testb %al, %al jne .L4 .loc 1 21 0 leaq -80(%rbp), %rax movq %rax, %rdi call g_get_current_time .loc 1 22 0 movq -80(%rbp), %rdx movq -64(%rbp), %rax movq %rdx, %rcx subq %rax, %rcx movq %rcx, %rax cvtsi2sdq %rax, %xmm0 movsd .LC0(%rip), %xmm1 mulsd %xmm0, %xmm1 movq -72(%rbp), %rax cvtsi2sdq %rax, %xmm0 addsd %xmm1, %xmm0 movq -56(%rbp), %rax cvtsi2sdq %rax, %xmm1 subsd %xmm1, %xmm0 movsd .LC1(%rip), %xmm1 divsd %xmm1, %xmm0 unpcklpd %xmm0, %xmm0 cvtpd2ps %xmm0, %xmm0 movss %xmm0, -28(%rbp) .loc 1 23 0 cvtsi2ss -20(%rbp), %xmm0 movss -28(%rbp), %xmm1 movaps %xmm1, %xmm2 divss %xmm0, %xmm2 movaps %xmm2, %xmm0 movss .LC2(%rip), %xmm1 mulss %xmm1, %xmm0 movss %xmm0, -32(%rbp) .loc 1 24 0 movss -32(%rbp), %xmm1 cvtps2pd %xmm1, %xmm1 movss -28(%rbp), %xmm0 cvtps2pd %xmm0, %xmm0 movl -20(%rbp), %edx leaq -224(%rbp), %rax movq %rax, %rsi movl $.LC3, %edi movl $2, %eax call g_print .LBE2: .LBB4: .loc 1 31 0 leaq -96(%rbp), %rax movq %rax, %rdi call g_get_current_time .loc 1 32 0 movl $1818847351, -224(%rbp) movl $695543909, -220(%rbp) movq $2960757, -216(%rbp) leaq -208(%rbp), %rdx movl $0, %eax movl $10, %ecx movq %rdx, %rdi rep stosq movq %rdi, %rdx movl %eax, (%rdx) addq $4, %rdx .loc 1 33 0 movl $100000, -36(%rbp) .loc 1 34 0 movl $500, -40(%rbp) .loc 1 35 0 movl -36(%rbp), %eax movl %eax, -12(%rbp) .loc 1 36 0 jmp .L5 .L8: .LBB5: .loc 1 38 0 movl -40(%rbp), %eax movl %eax, -16(%rbp) .loc 1 39 0 jmp .L6 .L7: .loc 1 39 0 is_stmt 0 discriminator 2 subl $1, -16(%rbp) .L6: .loc 1 39 0 discriminator 1 cmpl $0, -16(%rbp) jne .L7 .L5: .LBE5: .loc 1 36 0 is_stmt 1 discriminator 1 cmpl $0, -12(%rbp) setne %al subl $1, -12(%rbp) testb %al, %al jne .L8 .loc 1 41 0 leaq -112(%rbp), %rax movq %rax, %rdi call g_get_current_time .loc 1 42 0 movq -112(%rbp), %rdx movq -96(%rbp), %rax movq %rdx, %rcx subq %rax, %rcx movq %rcx, %rax cvtsi2sdq %rax, %xmm0 movsd .LC0(%rip), %xmm1 mulsd %xmm0, %xmm1 movq -104(%rbp), %rax cvtsi2sdq %rax, %xmm0 addsd %xmm1, %xmm0 movq -88(%rbp), %rax cvtsi2sdq %rax, %xmm1 subsd %xmm1, %xmm0 movsd .LC1(%rip), %xmm1 divsd %xmm1, %xmm0 unpcklpd %xmm0, %xmm0 cvtpd2ps %xmm0, %xmm0 movss %xmm0, -44(%rbp) .loc 1 43 0 cvtsi2ss -36(%rbp), %xmm0 movss -44(%rbp), %xmm1 movaps %xmm1, %xmm2 divss %xmm0, %xmm2 movaps %xmm2, %xmm0 movss .LC2(%rip), %xmm1 mulss %xmm1, %xmm0 movss %xmm0, -48(%rbp) .loc 1 44 0 movss -48(%rbp), %xmm1 cvtps2pd %xmm1, %xmm1 movss -44(%rbp), %xmm0 cvtps2pd %xmm0, %xmm0 movl -36(%rbp), %edx leaq -224(%rbp), %rax movq %rax, %rsi movl $.LC3, %edi movl $2, %eax call g_print .LBE4: .loc 1 46 0 movl $0, %eax .loc 1 47 0 leave .LCFI2: .cfi_def_cfa 7, 8 ret .cfi_endproc .LFE9: .size main, .-main .section .rodata .align 8 .LC0: .long 0 .long 1093567616 .align 8 .LC1: .long 0 .long 1083129856 .align 4 .LC2: .long 1232348160 .text .Letext0: .section .debug_loc,"",@progbits .Ldebug_loc0: .LLST0: .quad .LFB9-.Ltext0 .quad .LCFI0-.Ltext0 .value 0x2 .byte 0x77 .sleb128 8 .quad .LCFI0-.Ltext0 .quad .LCFI1-.Ltext0 .value 0x2 .byte 0x77 .sleb128 16 .quad .LCFI1-.Ltext0 .quad .LCFI2-.Ltext0 .value 0x2 .byte 0x76 .sleb128 16 .quad .LCFI2-.Ltext0 .quad .LFE9-.Ltext0 .value 0x2 .byte 0x77 .sleb128 8 .quad 0x0 .quad 0x0 .file 2 "/usr/include/glib-2.0/glib/gtypes.h" .section .debug_info .long 0x299 .value 0x2 .long .Ldebug_abbrev0 .byte 0x8 .uleb128 0x1 .long .LASF29 .byte 0x1 .string "a.c" .long .LASF30 .quad .Ltext0 .quad .Letext0 .long .Ldebug_line0 .uleb128 0x2 .byte 0x8 .byte 0x5 .long .LASF0 .uleb128 0x2 .byte 0x8 .byte 0x7 .long .LASF1 .uleb128 0x3 .byte 0x4 .byte 0x5 .string "int" .uleb128 0x2 .byte 0x1 .byte 0x6 .long .LASF2 .uleb128 0x2 .byte 0x1 .byte 0x8 .long .LASF3 .uleb128 0x2 .byte 0x2 .byte 0x5 .long .LASF4 .uleb128 0x2 .byte 0x2 .byte 0x7 .long .LASF5 .uleb128 0x2 .byte 0x4 .byte 0x7 .long .LASF6 .uleb128 0x4 .byte 0x8 .byte 0x7 .uleb128 0x2 .byte 0x1 .byte 0x6 .long .LASF7 .uleb128 0x2 .byte 0x8 .byte 0x4 .long .LASF8 .uleb128 0x5 .long .LASF9 .byte 0x2 .byte 0x2e .long 0x68 .uleb128 0x5 .long .LASF10 .byte 0x2 .byte 0x30 .long 0x2d .uleb128 0x5 .long .LASF11 .byte 0x2 .byte 0x31 .long 0x3b .uleb128 0x5 .long .LASF12 .byte 0x2 .byte 0x39 .long 0xa2 .uleb128 0x2 .byte 0x4 .byte 0x4 .long .LASF13 .uleb128 0x6 .long .LASF14 .byte 0x2 .value 0x1a2 .long 0xb5 .uleb128 0x7 .long .LASF31 .byte 0x10 .byte 0x2 .value 0x1a4 .long 0xe1 .uleb128 0x8 .long .LASF15 .byte 0x2 .value 0x1a6 .long 0x81 .byte 0x2 .byte 0x23 .uleb128 0x0 .uleb128 0x8 .long .LASF16 .byte 0x2 .value 0x1a7 .long 0x81 .byte 0x2 .byte 0x23 .uleb128 0x8 .byte 0x0 .uleb128 0x9 .byte 0x8 .long 0x68 .uleb128 0x2 .byte 0x8 .byte 0x7 .long .LASF17 .uleb128 0x2 .byte 0x8 .byte 0x5 .long .LASF18 .uleb128 0x2 .byte 0x10 .byte 0x4 .long .LASF19 .uleb128 0x9 .byte 0x8 .long 0xe1 .uleb128 0xa .byte 0x1 .long .LASF32 .byte 0x1 .byte 0x5 .byte 0x1 .long 0x3b .quad .LFB9 .quad .LFE9 .long .LLST0 .long 0x290 .uleb128 0xb .long .LASF20 .byte 0x1 .byte 0x5 .long 0x3b .byte 0x3 .byte 0x91 .sleb128 -244 .uleb128 0xb .long .LASF21 .byte 0x1 .byte 0x5 .long 0xfc .byte 0x3 .byte 0x91 .sleb128 -256 .uleb128 0xc .quad .LBB2 .quad .LBE2 .long 0x1ec .uleb128 0xd .long .LASF22 .byte 0x1 .byte 0xa .long 0xa9 .byte 0x3 .byte 0x91 .sleb128 -80 .uleb128 0xd .long .LASF23 .byte 0x1 .byte 0xa .long 0xa9 .byte 0x3 .byte 0x91 .sleb128 -96 .uleb128 0xe .string "str" .byte 0x1 .byte 0xc .long 0x290 .byte 0x3 .byte 0x91 .sleb128 -240 .uleb128 0xd .long .LASF24 .byte 0x1 .byte 0xd .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -36 .uleb128 0xd .long .LASF25 .byte 0x1 .byte 0xe .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -40 .uleb128 0xd .long .LASF26 .byte 0x1 .byte 0xf .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -20 .uleb128 0xd .long .LASF27 .byte 0x1 .byte 0x16 .long 0x97 .byte 0x2 .byte 0x91 .sleb128 -44 .uleb128 0xd .long .LASF28 .byte 0x1 .byte 0x17 .long 0x97 .byte 0x2 .byte 0x91 .sleb128 -48 .uleb128 0xf .quad .LBB3 .quad .LBE3 .uleb128 0xe .string "u" .byte 0x1 .byte 0x12 .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -24 .byte 0x0 .byte 0x0 .uleb128 0xf .quad .LBB4 .quad .LBE4 .uleb128 0xd .long .LASF22 .byte 0x1 .byte 0x1e .long 0xa9 .byte 0x3 .byte 0x91 .sleb128 -112 .uleb128 0xd .long .LASF23 .byte 0x1 .byte 0x1e .long 0xa9 .byte 0x3 .byte 0x91 .sleb128 -128 .uleb128 0xe .string "str" .byte 0x1 .byte 0x20 .long 0x290 .byte 0x3 .byte 0x91 .sleb128 -240 .uleb128 0xd .long .LASF24 .byte 0x1 .byte 0x21 .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -52 .uleb128 0xd .long .LASF25 .byte 0x1 .byte 0x22 .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -56 .uleb128 0xd .long .LASF26 .byte 0x1 .byte 0x23 .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -28 .uleb128 0xd .long .LASF27 .byte 0x1 .byte 0x2a .long 0x97 .byte 0x2 .byte 0x91 .sleb128 -60 .uleb128 0xd .long .LASF28 .byte 0x1 .byte 0x2b .long 0x97 .byte 0x2 .byte 0x91 .sleb128 -64 .uleb128 0xf .quad .LBB5 .quad .LBE5 .uleb128 0xe .string "u" .byte 0x1 .byte 0x26 .long 0x8c .byte 0x2 .byte 0x91 .sleb128 -32 .byte 0x0 .byte 0x0 .byte 0x0 .uleb128 0x10 .long 0x76 .uleb128 0x11 .long 0x65 .byte 0x63 .byte 0x0 .byte 0x0 .section .debug_abbrev .uleb128 0x1 .uleb128 0x11 .byte 0x1 .uleb128 0x25 .uleb128 0xe .uleb128 0x13 .uleb128 0xb .uleb128 0x3 .uleb128 0x8 .uleb128 0x1b .uleb128 0xe .uleb128 0x11 .uleb128 0x1 .uleb128 0x12 .uleb128 0x1 .uleb128 0x10 .uleb128 0x6 .byte 0x0 .byte 0x0 .uleb128 0x2 .uleb128 0x24 .byte 0x0 .uleb128 0xb .uleb128 0xb .uleb128 0x3e .uleb128 0xb .uleb128 0x3 .uleb128 0xe .byte 0x0 .byte 0x0 .uleb128 0x3 .uleb128 0x24 .byte 0x0 .uleb128 0xb .uleb128 0xb .uleb128 0x3e .uleb128 0xb .uleb128 0x3 .uleb128 0x8 .byte 0x0 .byte 0x0 .uleb128 0x4 .uleb128 0x24 .byte 0x0 .uleb128 0xb .uleb128 0xb .uleb128 0x3e .uleb128 0xb .byte 0x0 .byte 0x0 .uleb128 0x5 .uleb128 0x16 .byte 0x0 .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0xb .uleb128 0x49 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0x6 .uleb128 0x16 .byte 0x0 .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0x5 .uleb128 0x49 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0x7 .uleb128 0x13 .byte 0x1 .uleb128 0x3 .uleb128 0xe .uleb128 0xb .uleb128 0xb .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0x5 .uleb128 0x1 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0x8 .uleb128 0xd .byte 0x0 .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0x5 .uleb128 0x49 .uleb128 0x13 .uleb128 0x38 .uleb128 0xa .byte 0x0 .byte 0x0 .uleb128 0x9 .uleb128 0xf .byte 0x0 .uleb128 0xb .uleb128 0xb .uleb128 0x49 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0xa .uleb128 0x2e .byte 0x1 .uleb128 0x3f .uleb128 0xc .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0xb .uleb128 0x27 .uleb128 0xc .uleb128 0x49 .uleb128 0x13 .uleb128 0x11 .uleb128 0x1 .uleb128 0x12 .uleb128 0x1 .uleb128 0x40 .uleb128 0x6 .uleb128 0x1 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0xb .uleb128 0x5 .byte 0x0 .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0xb .uleb128 0x49 .uleb128 0x13 .uleb128 0x2 .uleb128 0xa .byte 0x0 .byte 0x0 .uleb128 0xc .uleb128 0xb .byte 0x1 .uleb128 0x11 .uleb128 0x1 .uleb128 0x12 .uleb128 0x1 .uleb128 0x1 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0xd .uleb128 0x34 .byte 0x0 .uleb128 0x3 .uleb128 0xe .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0xb .uleb128 0x49 .uleb128 0x13 .uleb128 0x2 .uleb128 0xa .byte 0x0 .byte 0x0 .uleb128 0xe .uleb128 0x34 .byte 0x0 .uleb128 0x3 .uleb128 0x8 .uleb128 0x3a .uleb128 0xb .uleb128 0x3b .uleb128 0xb .uleb128 0x49 .uleb128 0x13 .uleb128 0x2 .uleb128 0xa .byte 0x0 .byte 0x0 .uleb128 0xf .uleb128 0xb .byte 0x1 .uleb128 0x11 .uleb128 0x1 .uleb128 0x12 .uleb128 0x1 .byte 0x0 .byte 0x0 .uleb128 0x10 .uleb128 0x1 .byte 0x1 .uleb128 0x49 .uleb128 0x13 .byte 0x0 .byte 0x0 .uleb128 0x11 .uleb128 0x21 .byte 0x0 .uleb128 0x49 .uleb128 0x13 .uleb128 0x2f .uleb128 0xb .byte 0x0 .byte 0x0 .byte 0x0 .section .debug_pubnames,"",@progbits .long 0x17 .value 0x2 .long .Ldebug_info0 .long 0x29d .long 0x102 .string "main" .long 0x0 .section .debug_pubtypes,"",@progbits .long 0x51 .value 0x2 .long .Ldebug_info0 .long 0x29d .long 0x76 .string "gchar" .long 0x81 .string "glong" .long 0x8c .string "gint" .long 0x97 .string "gfloat" .long 0xa9 .string "GTimeVal" .long 0xb5 .string "_GTimeVal" .long 0x0 .section .debug_aranges,"",@progbits .long 0x2c .value 0x2 .long .Ldebug_info0 .byte 0x8 .byte 0x0 .value 0x0 .value 0x0 .quad .Ltext0 .quad .Letext0-.Ltext0 .quad 0x0 .quad 0x0 .section .debug_str,"MS",@progbits,1 .LASF13: .string "float" .LASF12: .string "gfloat" .LASF9: .string "gchar" .LASF29: .string "GNU C 4.5.0 20100604 [gcc-4_5-branch revision 160292]" .LASF10: .string "glong" .LASF24: .string "loops" .LASF3: .string "unsigned char" .LASF26: .string "loops_cpy" .LASF1: .string "long unsigned int" .LASF5: .string "short unsigned int" .LASF22: .string "tStart" .LASF8: .string "double" .LASF32: .string "main" .LASF15: .string "tv_sec" .LASF6: .string "unsigned int" .LASF14: .string "GTimeVal" .LASF30: .string "/root/Desktop/xudong/workhome_gtk/test_while" .LASF16: .string "tv_usec" .LASF31: .string "_GTimeVal" .LASF11: .string "gint" .LASF27: .string "time_msec" .LASF20: .string "argc" .LASF23: .string "tEnd" .LASF18: .string "long long int" .LASF28: .string "time_each" .LASF7: .string "char" .LASF4: .string "short int" .LASF21: .string "argv" .LASF0: .string "long int" .LASF19: .string "long double" .LASF25: .string "u_org" .LASF2: .string "signed char" .LASF17: .string "long long unsigned int" .ident "GCC: (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch revision 160292]" .section .comment.SUSE.OPTs,"MS",@progbits,1 .string "ospWG" .section .note.GNU-stack,"",@progbits