1 /*===-- udivsi3.S - 32-bit unsigned integer divide ------------------------===// 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 __udivsi3 (32-bit unsigned integer divide) 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 ESTABLISH_FRAME \ 19 push {r7, lr} ;\ 20 mov r7, sp 21 #define CLEAR_FRAME_AND_RETURN \ 22 pop {r7, pc} 23 24 #define a r0 25 #define b r1 26 #define r r2 27 #define i r3 28 #define q ip 29 #define one lr 30 31 .syntax unified 32 .align 3 33 // Ok, APCS and AAPCS agree on 32 bit args, so it's safe to use the same routine. 34 DEFINE_AEABI_FUNCTION_ALIAS(__aeabi_uidiv, __udivsi3) 35 DEFINE_COMPILERRT_FUNCTION(__udivsi3) 36 #if __ARM_ARCH_7S__ 37 tst r1,r1 38 beq LOCAL_LABEL(divzero) 39 udiv r0, r0, r1 40 bx lr 41 LOCAL_LABEL(divzero): 42 mov r0,#0 43 bx lr 44 #else 45 // We use a simple digit by digit algorithm; before we get into the actual 46 // divide loop, we must calculate the left-shift amount necessary to align 47 // the MSB of the divisor with that of the dividend (If this shift is 48 // negative, then the result is zero, and we early out). We also conjure a 49 // bit mask of 1 to use in constructing the quotient, and initialize the 50 // quotient to zero. 51 ESTABLISH_FRAME 52 clz r2, a 53 tst b, b // detect divide-by-zero 54 clz r3, b 55 mov q, #0 56 beq LOCAL_LABEL(return) // return 0 if b is zero. 57 mov one, #1 58 subs i, r3, r2 59 blt LOCAL_LABEL(return) // return 0 if MSB(a) < MSB(b) 60 61 LOCAL_LABEL(mainLoop): 62 // This loop basically implements the following: 63 // 64 // do { 65 // if (a >= b << i) { 66 // a -= b << i; 67 // q |= 1 << i; 68 // if (a == 0) break; 69 // } 70 // } while (--i) 71 // 72 // Note that this does not perform the final iteration (i == 0); by doing it 73 // this way, we can merge the two branches which is a substantial win for 74 // such a tight loop on current ARM architectures. 75 subs r, a, b, lsl i 76 orrhs q, q,one, lsl i 77 movhs a, r 78 subsne i, i, #1 79 bhi LOCAL_LABEL(mainLoop) 80 81 // Do the final test subtraction and update of quotient (i == 0), as it is 82 // not performed in the main loop. 83 subs r, a, b 84 orrhs q, #1 85 86 LOCAL_LABEL(return): 87 // Move the quotient to r0 and return. 88 mov r0, q 89 CLEAR_FRAME_AND_RETURN 90 #endif 91
