I am analysing how switch is converted from C to aseembly (GAS). I don't understand the GAS's trick how the 'lower edge' default is triggered.

There is a conditional jump for 'higher edge' :

cmpl    $8, %eaxja  .L2

There is no conditional jump for 'lower edge', just a jump into jump table

So, how is the 'lower' default handled?e.g. when i input 10 - DEFAULT is displayed

-----------part of code where I think the trick is hidden(switch's range is 11-19, uneven numbers)

    call    scanf              #switch argument is in %eax    movl    -4(%rbp), %eax     subl    $11, %eax    cmpl    $8, %eax    ja  .L2                   # higher edge default    movl    %eax, %eax    leaq    0(,%rax,4), %rdx    leaq    .L4(%rip), %rax    movl    (%rdx,%rax), %eax    movslq  %eax, %rdx    leaq    .L4(%rip), %rax    addq    %rdx, %rax    jmp *%rax

-----------below is source code

C code :

#include <stdio.h>int main(){    int a;    printf("Insert a number : ");    scanf("%d",&a);    switch(a)    {        case 11:             printf("ELEVEN\n");            break;        case 13:            printf("THIRTEEN\n");            break;        case 15:            printf("FIFTEEN\n");            break;        case 17:            printf("SEVENTEEN\n");            break;        case 19:            printf("NINETEEN\n");            break;        default:            printf("DEFAULT\n");            break;    }    return 0;}

GAS code:

    .file   "switch1.c"    .text    .def    __main; .scl    2;  .type   32; .endef    .section .rdata,"dr".LC0:    .ascii "Insert a number : \0".LC1:    .ascii "%d\0".LC2:    .ascii "ELEVEN\0".LC3:    .ascii "THIRTEEN\0".LC4:    .ascii "FIFTEEN\0".LC5:    .ascii "SEVENTEEN\0".LC6:    .ascii "NINETEEN\0".LC7:    .ascii "DEFAULT\0"    .text    .globl  main    .def    main;   .scl    2;  .type   32; .endef    .seh_proc   mainmain:    pushq   %rbp    .seh_pushreg    %rbp    movq    %rsp, %rbp    .seh_setframe   %rbp, 0    subq    $48, %rsp    .seh_stackalloc 48    .seh_endprologue    call    __main    leaq    .LC0(%rip), %rcx    call    printf    leaq    -4(%rbp), %rax    movq    %rax, %rdx    leaq    .LC1(%rip), %rcx    call    scanf    movl    -4(%rbp), %eax    subl    $11, %eax    cmpl    $8, %eax    ja  .L2    movl    %eax, %eax    leaq    0(,%rax,4), %rdx    leaq    .L4(%rip), %rax    movl    (%rdx,%rax), %eax    movslq  %eax, %rdx    leaq    .L4(%rip), %rax    addq    %rdx, %rax    jmp *%rax    .section .rdata,"dr"    .align 4.L4:    .long   .L3-.L4    .long   .L2-.L4    .long   .L5-.L4    .long   .L2-.L4    .long   .L6-.L4    .long   .L2-.L4    .long   .L7-.L4    .long   .L2-.L4    .long   .L8-.L4    .text.L3:    leaq    .LC2(%rip), %rcx    call    puts    jmp .L9.L5:    leaq    .LC3(%rip), %rcx    call    puts    jmp .L9.L6:    leaq    .LC4(%rip), %rcx    call    puts    jmp .L9.L7:    leaq    .LC5(%rip), %rcx    call    puts    jmp .L9.L8:    leaq    .LC6(%rip), %rcx    call    puts    jmp .L9.L2:    leaq    .LC7(%rip), %rcx    call    puts    nop.L9:    movl    $0, %eax    addq    $48, %rsp    popq    %rbp    ret    .seh_endproc    .ident  "GCC: (GNU) 7.4.0"    .def    printf; .scl    2;  .type   32; .endef    .def    scanf;  .scl    2;  .type   32; .endef    .def    puts;   .scl    2;  .type   32; .endef