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#               The Compcert verified compiler
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#           Xavier Leroy, INRIA Paris-Rocquencourt
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# Helper functions for 64-bit integer arithmetic.  IA32 version.
	
# Division and remainder

# Auxiliary function, never called directly from C code
# Input:   20(esp), 24(esp)  is dividend N
#          28(esp), 32(esp)  is divisor  D
# Output:  esi:edi is quotient Q
#          eax:edx is remainder R
# ebp is preserved

        .text
	.globl  __i64_udivmod
        .balign 16
__i64_udivmod:
        cmpl $0, 32(%esp)        # single-word divisor? (DH = 0)
        jne 1f
  # Special case 64 bits divided by 32 bits
        movl 28(%esp), %ecx      # divide NH by DL
        movl 24(%esp), %eax      # (will trap if D = 0)
        xorl %edx, %edx
        divl %ecx                # eax = quotient, edx = remainder
        movl %eax, %edi          # high word of quotient in edi
        movl 20(%esp), %eax      # divide rem : NL by DL
        divl %ecx                # eax = quotient, edx = remainder
        movl %eax, %esi          # low word of quotient in esi */
        movl %edx, %eax          # low word of remainder in eax
        xorl %edx, %edx          # high word of remainder is 0, in edx
        ret
  # The general case
1:      movl 28(%esp), %ecx      # esi:ecx = D
        movl 32(%esp), %esi
        movl 20(%esp), %eax      # edx:eax = N
        movl 24(%esp), %edx
  # Scale D and N down, giving D' and N', until D' fits in 32 bits
2:      shrl $1, %esi            # shift D' right by one
        rcrl $1, %ecx
        shrl $1, %edx            # shift N' right by one
        rcrl $1, %eax
        testl %esi, %esi         # repeat until D'H = 0
        jnz 2b
  # Divide N' by D' to get an approximate quotient
        divl %ecx                # eax = quotient, edx = remainder
        movl %eax, %esi          # save tentative quotient Q in esi
  # Check for off by one quotient
  # Compute Q * D
3:      movl 32(%esp), %ecx
        imull %esi, %ecx         # ecx = Q * DH
        movl 28(%esp), %eax
        mull %esi                # edx:eax = Q * DL
        add %ecx, %edx           # edx:eax = Q * D
        jc 5f                    # overflow in addition means Q is too high
  # Compare Q * D with N, computing the remainder in the process
        movl %eax, %ecx
        movl 20(%esp), %eax
        subl %ecx, %eax
        movl %edx, %ecx
        movl 24(%esp), %edx
        sbbl %ecx, %edx          # edx:eax = N - Q * D
        jnc 4f                   # no carry: N >= Q * D, we are fine
        decl %esi                # carry: N < Q * D, adjust Q down by 1
        addl 28(%esp), %eax      # and remainder up by D
        adcl 32(%esp), %edx
  # Finished
4:      xorl %edi, %edi          # high half of quotient is 0
        ret
  # Special case when Q * D overflows
5:      decl %esi                # adjust Q down by 1
        jmp 3b                   # and redo check & computation of remainder

        .type __i64_udivmod, @function
        .size __i64_udivmod, . - __i64_udivmod