Dividing by Multiplying

I am having a litle trouble understanding how this code works.

C code:

Code:

 
#include <stdio.h>

unsigned long foo( unsigned long a)
{

        unsigned long b;

        b = a / 10;

        return b; 

}

int main()
{        

        foo(100);                        
        return 0; 
}

vc++ optimized code:

Code:

 
PUBLIC  _foo
; Function compile flags: /Ogtpy
;       COMDAT _foo
_TEXT   SEGMENT
_a$ = 8                                                 ; size = 4
_foo    PROC                                            ; COMDAT
; File c:\documents and settings\kelvin\my documents\code\div.c
; Line 9
        mov     eax, -858993459                         ; cccccccdH
        mul     DWORD PTR _a$[esp-4]
        shr     edx, 3
; Line 11
        mov     eax, edx
; Line 13
        ret     0
_foo    ENDP

I understand how the result is produced but I don't quite understand the mathematical principles. In particular how does the compiler come up with
cccccccdH? Any ideas?