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/*===-- udivmodsi4.S - 32-bit unsigned integer divide and modulus ---------===//
*
* The LLVM Compiler Infrastructure
*
* This file is dual licensed under the MIT and the University of Illinois Open
* Source Licenses. See LICENSE.TXT for details.
*
*===----------------------------------------------------------------------===//
*
* This file implements the __udivmodsi4 (32-bit unsigned integer divide and
* modulus) function for the ARM architecture. A naive digit-by-digit
* computation is employed for simplicity.
*
*===----------------------------------------------------------------------===*/
#include "../assembly.h"
#define ESTABLISH_FRAME \
push {r4, r7, lr} ;\
add r7, sp, #4
#define CLEAR_FRAME_AND_RETURN \
pop {r4, r7, pc}
#define a r0
#define b r1
#define i r3
#define r r4
#define q ip
#define one lr
.syntax unified
.align 3
DEFINE_COMPILERRT_FUNCTION(__udivmodsi4)
#if __ARM_ARCH_EXT_IDIV__
tst r1, r1
beq LOCAL_LABEL(divzero)
mov r3, r0
udiv r0, r3, r1
mls r1, r0, r1, r3
str r1, [r2]
bx lr
LOCAL_LABEL(divzero):
mov r0, #0
bx lr
#else
// We use a simple digit by digit algorithm; before we get into the actual
// divide loop, we must calculate the left-shift amount necessary to align
// the MSB of the divisor with that of the dividend (If this shift is
// negative, then the result is zero, and we early out). We also conjure a
// bit mask of 1 to use in constructing the quotient, and initialize the
// quotient to zero.
ESTABLISH_FRAME
clz r4, a
tst b, b // detect divide-by-zero
clz r3, b
mov q, #0
beq LOCAL_LABEL(return) // return 0 if b is zero.
mov one, #1
subs i, r3, r4
blt LOCAL_LABEL(return) // return 0 if MSB(a) < MSB(b)
LOCAL_LABEL(mainLoop):
// This loop basically implements the following:
//
// do {
// if (a >= b << i) {
// a -= b << i;
// q |= 1 << i;
// if (a == 0) break;
// }
// } while (--i)
//
// Note that this does not perform the final iteration (i == 0); by doing it
// this way, we can merge the two branches which is a substantial win for
// such a tight loop on current ARM architectures.
subs r, a, b, lsl i
orrhs q, q,one, lsl i
movhs a, r
subsne i, i, #1
bhi LOCAL_LABEL(mainLoop)
// Do the final test subtraction and update of quotient (i == 0), as it is
// not performed in the main loop.
subs r, a, b
orrhs q, #1
movhs a, r
LOCAL_LABEL(return):
// Store the remainder, and move the quotient to r0, then return.
str a, [r2]
mov r0, q
CLEAR_FRAME_AND_RETURN
#endif
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