1 /*===-- umodsi3.S - 32-bit unsigned integer modulus -----------------------===// 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is dual licensed under the MIT and the University of Illinois Open 6 * Source Licenses. See LICENSE.TXT for details. 7 * 8 *===----------------------------------------------------------------------===// 9 * 10 * This file implements the __umodsi3 (32-bit unsigned integer modulus) 11 * function for the ARM architecture. A naive digit-by-digit computation is 12 * employed for simplicity. 13 * 14 *===----------------------------------------------------------------------===*/ 15 16 #include "../assembly.h" 17 18 #define a r0 19 #define b r1 20 #define r r2 21 #define i r3 22 23 .syntax unified 24 .align 3 25 DEFINE_COMPILERRT_FUNCTION(__umodsi3) 26 // We use a simple digit by digit algorithm; before we get into the actual 27 // divide loop, we must calculate the left-shift amount necessary to align 28 // the MSB of the divisor with that of the dividend. 29 clz r2, a 30 tst b, b // detect b == 0 31 clz r3, b 32 bxeq lr // return a if b == 0 33 subs i, r3, r2 34 bxlt lr // return a if MSB(a) < MSB(b) 35 36 LOCAL_LABEL(mainLoop): 37 // This loop basically implements the following: 38 // 39 // do { 40 // if (a >= b << i) { 41 // a -= b << i; 42 // if (a == 0) break; 43 // } 44 // } while (--i) 45 // 46 // Note that this does not perform the final iteration (i == 0); by doing it 47 // this way, we can merge the two branches which is a substantial win for 48 // such a tight loop on current ARM architectures. 49 subs r, a, b, lsl i 50 movhs a, r 51 subsne i, i, #1 52 bhi LOCAL_LABEL(mainLoop) 53 54 // Do the final test subtraction and update of remainder (i == 0), as it is 55 // not performed in the main loop. 56 subs r, a, b 57 movhs a, r 58 bx lr 59
