toaruos/util/compiler-rt.S

518 lines
23 KiB
ArmAsm

// This file contains assembly implementations of:
// __udivdi3
// __umoddi3
// ... from LLVM's compiler-rt, for use with building
// the ToaruOS kernel with a bare clang, with no need to link
// to libgcc or compiler-rt directly. If more function
// implementations are needed in the future, these should also
// be included here.
// ==============================================================================
// The LLVM Project is under the Apache License v2.0 with LLVM Exceptions:
// ==============================================================================
//
// Apache License
// Version 2.0, January 2004
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.text
.balign 4
.globl __udivdi3
__udivdi3:
pushl %ebx
movl 20(%esp), %ebx // Find the index i of the leading bit in b.
bsrl %ebx, %ecx // If the high word of b is zero, jump to
jz 9f // the code to handle that special case [9].
// High word of b is known to be non-zero on this branch
movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
shrl %cl, %eax // Practically, this means that bhi is given by:
shrl %eax //
notl %ecx // bhi = (high word of b) << (31 - i) |
shll %cl, %ebx // (low word of b) >> (1 + i)
orl %eax, %ebx //
movl 12(%esp), %edx // Load the high and low words of a, and jump
movl 8(%esp), %eax // to [1] if the high word is larger than bhi
cmpl %ebx, %edx // to avoid overflowing the upcoming divide.
jae 1f
// High word of a is greater than or equal to (b >> (1 + i)) on this branch
divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
pushl %edi
notl %ecx
shrl %eax
shrl %cl, %eax // q = qs >> (1 + i)
movl %eax, %edi
mull 20(%esp) // q*blo
movl 12(%esp), %ebx
movl 16(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 24(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
sbbl $0, %edi // decrement q if remainder is negative
xorl %edx, %edx
movl %edi, %eax
popl %edi
popl %ebx
retl
1: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
subl %ebx, %edx // subtract bhi from ahi so that divide will not
divl %ebx // overflow, and find q and r such that
//
// ahi:alo = (1:q)*bhi + r
//
// Note that q is a number in (31-i).(1+i)
// fix point.
pushl %edi
notl %ecx
shrl %eax
orl $0x80000000, %eax
shrl %cl, %eax // q = (1:qs) >> (1 + i)
movl %eax, %edi
mull 20(%esp) // q*blo
movl 12(%esp), %ebx
movl 16(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 24(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
sbbl $0, %edi // decrement q if remainder is negative
xorl %edx, %edx
movl %edi, %eax
popl %edi
popl %ebx
retl
9: // High word of b is zero on this branch
movl 12(%esp), %eax // Find qhi and rhi such that
movl 16(%esp), %ecx //
xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b
divl %ecx //
movl %eax, %ebx //
movl 8(%esp), %eax // Find qlo such that
divl %ecx //
movl %ebx, %edx // rhi:alo = qlo*b + rlo with 0 rlo < b
popl %ebx //
retl // and return qhi:qlo
.text
.balign 4
.globl __umoddi3
__umoddi3:
pushl %ebx
movl 20(%esp), %ebx // Find the index i of the leading bit in b.
bsrl %ebx, %ecx // If the high word of b is zero, jump to
jz 9f // the code to handle that special case [9].
// High word of b is known to be non-zero on this branch
movl 16(%esp), %eax // Construct bhi, containing bits [1+i:32+i] of b
shrl %cl, %eax // Practically, this means that bhi is given by:
shrl %eax //
notl %ecx // bhi = (high word of b) << (31 - i) |
shll %cl, %ebx // (low word of b) >> (1 + i)
orl %eax, %ebx //
movl 12(%esp), %edx // Load the high and low words of a, and jump
movl 8(%esp), %eax // to [2] if the high word is larger than bhi
cmpl %ebx, %edx // to avoid overflowing the upcoming divide.
jae 2f
// High word of a is greater than or equal to (b >> (1 + i)) on this branch
divl %ebx // eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
pushl %edi
notl %ecx
shrl %eax
shrl %cl, %eax // q = qs >> (1 + i)
movl %eax, %edi
mull 20(%esp) // q*blo
movl 12(%esp), %ebx
movl 16(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 24(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
jnc 1f // if positive, this is the result.
addl 20(%esp), %ebx // otherwise
adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
1: movl %ebx, %eax
movl %ecx, %edx
popl %edi
popl %ebx
retl
2: // High word of a is greater than or equal to (b >> (1 + i)) on this branch
subl %ebx, %edx // subtract bhi from ahi so that divide will not
divl %ebx // overflow, and find q and r such that
//
// ahi:alo = (1:q)*bhi + r
//
// Note that q is a number in (31-i).(1+i)
// fix point.
pushl %edi
notl %ecx
shrl %eax
orl $0x80000000, %eax
shrl %cl, %eax // q = (1:qs) >> (1 + i)
movl %eax, %edi
mull 20(%esp) // q*blo
movl 12(%esp), %ebx
movl 16(%esp), %ecx // ECX:EBX = a
subl %eax, %ebx
sbbl %edx, %ecx // ECX:EBX = a - q*blo
movl 24(%esp), %eax
imull %edi, %eax // q*bhi
subl %eax, %ecx // ECX:EBX = a - q*b
jnc 3f // if positive, this is the result.
addl 20(%esp), %ebx // otherwise
adcl 24(%esp), %ecx // ECX:EBX = a - (q-1)*b = result
3: movl %ebx, %eax
movl %ecx, %edx
popl %edi
popl %ebx
retl
9: // High word of b is zero on this branch
movl 12(%esp), %eax // Find qhi and rhi such that
movl 16(%esp), %ecx //
xorl %edx, %edx // ahi = qhi*b + rhi with 0 rhi < b
divl %ecx //
movl %eax, %ebx //
movl 8(%esp), %eax // Find rlo such that
divl %ecx //
movl %edx, %eax // rhi:alo = qlo*b + rlo with 0 rlo < b
popl %ebx //
xorl %edx, %edx // and return 0:rlo
retl //