blob: 97e904315ec6491bafb121ef79749e8d04b67645 [file] [log] [blame]
 /* * Copyright 2004-2009 Analog Devices Inc. * * Licensed under the ADI BSD license or the GPL-2 (or later) */ #include #define CARRY AC0 #ifdef CONFIG_ARITHMETIC_OPS_L1 .section .l1.text #else .text #endif ENTRY(___udivsi3) CC = R0 < R1 (IU); /* If X < Y, always return 0 */ IF CC JUMP .Lreturn_ident; R2 = R1 << 16; CC = R2 <= R0 (IU); IF CC JUMP .Lidents; R2 = R0 >> 31; /* if X is a 31-bit number */ R3 = R1 >> 15; /* and Y is a 15-bit number */ R2 = R2 | R3; /* then it's okay to use the DIVQ builtins (fallthrough to fast)*/ CC = R2; IF CC JUMP .Ly_16bit; /* METHOD 1: FAST DIVQ We know we have a 31-bit dividend, and 15-bit divisor so we can use the simple divq approach (first setting AQ to 0 - implying unsigned division, then 16 DIVQ's). */ AQ = CC; /* Clear AQ (CC==0) */ /* ISR States: When dividing two integers (32.0/16.0) using divide primitives, we need to shift the dividend one bit to the left. We have already checked that we have a 31-bit number so we are safe to do that. */ R0 <<= 1; DIVQ(R0, R1); // 1 DIVQ(R0, R1); // 2 DIVQ(R0, R1); // 3 DIVQ(R0, R1); // 4 DIVQ(R0, R1); // 5 DIVQ(R0, R1); // 6 DIVQ(R0, R1); // 7 DIVQ(R0, R1); // 8 DIVQ(R0, R1); // 9 DIVQ(R0, R1); // 10 DIVQ(R0, R1); // 11 DIVQ(R0, R1); // 12 DIVQ(R0, R1); // 13 DIVQ(R0, R1); // 14 DIVQ(R0, R1); // 15 DIVQ(R0, R1); // 16 R0 = R0.L (Z); RTS; .Ly_16bit: /* We know that the upper 17 bits of Y might have bits set, ** or that the sign bit of X might have a bit. If Y is a ** 16-bit number, but not bigger, then we can use the builtins ** with a post-divide correction. ** R3 currently holds Y>>15, which means R3's LSB is the ** bit we're interested in. */ /* According to the ISR, to use the Divide primitives for ** unsigned integer divide, the useable range is 31 bits */ CC = ! BITTST(R0, 31); /* IF condition is true we can scale our inputs and use the divide primitives, ** with some post-adjustment */ R3 += -1; /* if so, Y is 0x00008nnn */ CC &= AZ; /* If condition is true we can scale our inputs and use the divide primitives, ** with some post-adjustment */ R3 = R1 >> 1; /* Pre-scaled divisor for primitive case */ R2 = R0 >> 16; R2 = R3 - R2; /* shifted divisor < upper 16 bits of dividend */ CC &= CARRY; IF CC JUMP .Lshift_and_correct; /* Fall through to the identities */ /* METHOD 2: identities and manual calculation We are not able to use the divide primites, but may still catch some special cases. */ .Lidents: /* Test for common identities. Value to be returned is placed in R2. */ CC = R0 == 0; /* 0/Y => 0 */ IF CC JUMP .Lreturn_r0; CC = R0 == R1; /* X==Y => 1 */ IF CC JUMP .Lreturn_ident; CC = R1 == 1; /* X/1 => X */ IF CC JUMP .Lreturn_ident; R2.L = ONES R1; R2 = R2.L (Z); CC = R2 == 1; IF CC JUMP .Lpower_of_two; [--SP] = (R7:5); /* Push registers R5-R7 */ /* Idents don't match. Go for the full operation. */ R6 = 2; /* assume we'll shift two */ R3 = 1; P2 = R1; /* If either R0 or R1 have sign set, */ /* divide them by two, and note it's */ /* been done. */ CC = R1 < 0; R2 = R1 >> 1; IF CC R1 = R2; /* Possibly-shifted R1 */ IF !CC R6 = R3; /* R1 doesn't, so at most 1 shifted */ P0 = 0; R3 = -R1; [--SP] = R3; R2 = R0 >> 1; R2 = R0 >> 1; CC = R0 < 0; IF CC P0 = R6; /* Number of values divided */ IF !CC R2 = R0; /* Shifted R0 */ /* P0 is 0, 1 (NR/=2) or 2 (NR/=2, DR/=2) */ /* r2 holds Copy dividend */ R3 = 0; /* Clear partial remainder */ R7 = 0; /* Initialise quotient bit */ P1 = 32; /* Set loop counter */ LSETUP(.Lulst, .Lulend) LC0 = P1; /* Set loop counter */ .Lulst: R6 = R2 >> 31; /* R6 = sign bit of R2, for carry */ R2 = R2 << 1; /* Shift 64 bit dividend up by 1 bit */ R3 = R3 << 1 || R5 = [SP]; R3 = R3 | R6; /* Include any carry */ CC = R7 < 0; /* Check quotient(AQ) */ /* If AQ==0, we'll sub divisor */ IF CC R5 = R1; /* and if AQ==1, we'll add it. */ R3 = R3 + R5; /* Add/sub divsor to partial remainder */ R7 = R3 ^ R1; /* Generate next quotient bit */ R5 = R7 >> 31; /* Get AQ */ BITTGL(R5, 0); /* Invert it, to get what we'll shift */ .Lulend: R2 = R2 + R5; /* and "shift" it in. */ CC = P0 == 0; /* Check how many inputs we shifted */ IF CC JUMP .Lno_mult; /* if none... */ R6 = R2 << 1; CC = P0 == 1; IF CC R2 = R6; /* if 1, Q = Q*2 */ IF !CC R1 = P2; /* if 2, restore stored divisor */ R3 = R2; /* Copy of R2 */ R3 *= R1; /* Q * divisor */ R5 = R0 - R3; /* Z = (dividend - Q * divisor) */ CC = R1 <= R5 (IU); /* Check if divisor <= Z? */ R6 = CC; /* if yes, R6 = 1 */ R2 = R2 + R6; /* if yes, add one to quotient(Q) */ .Lno_mult: SP += 4; (R7:5) = [SP++]; /* Pop registers R5-R7 */ R0 = R2; /* Store quotient */ RTS; .Lreturn_ident: CC = R0 < R1 (IU); /* If X < Y, always return 0 */ R2 = 0; IF CC JUMP .Ltrue_return_ident; R2 = -1 (X); /* X/0 => 0xFFFFFFFF */ CC = R1 == 0; IF CC JUMP .Ltrue_return_ident; R2 = -R2; /* R2 now 1 */ CC = R0 == R1; /* X==Y => 1 */ IF CC JUMP .Ltrue_return_ident; R2 = R0; /* X/1 => X */ /*FALLTHRU*/ .Ltrue_return_ident: R0 = R2; .Lreturn_r0: RTS; .Lpower_of_two: /* Y has a single bit set, which means it's a power of two. ** That means we can perform the division just by shifting ** X to the right the appropriate number of bits */ /* signbits returns the number of sign bits, minus one. ** 1=>30, 2=>29, ..., 0x40000000=>0. Which means we need ** to shift right n-signbits spaces. It also means 0x80000000 ** is a special case, because that *also* gives a signbits of 0 */ R2 = R0 >> 31; CC = R1 < 0; IF CC JUMP .Ltrue_return_ident; R1.l = SIGNBITS R1; R1 = R1.L (Z); R1 += -30; R0 = LSHIFT R0 by R1.L; RTS; /* METHOD 3: PRESCALE AND USE THE DIVIDE PRIMITIVES WITH SOME POST-CORRECTION Two scaling operations are required to use the divide primitives with a divisor > 0x7FFFF. Firstly (as in method 1) we need to shift the dividend 1 to the left for integer division. Secondly we need to shift both the divisor and dividend 1 to the right so both are in range for the primitives. The left/right shift of the dividend does nothing so we can skip it. */ .Lshift_and_correct: R2 = R0; // R3 is already R1 >> 1 CC=!CC; AQ = CC; /* Clear AQ, got here with CC = 0 */ DIVQ(R2, R3); // 1 DIVQ(R2, R3); // 2 DIVQ(R2, R3); // 3 DIVQ(R2, R3); // 4 DIVQ(R2, R3); // 5 DIVQ(R2, R3); // 6 DIVQ(R2, R3); // 7 DIVQ(R2, R3); // 8 DIVQ(R2, R3); // 9 DIVQ(R2, R3); // 10 DIVQ(R2, R3); // 11 DIVQ(R2, R3); // 12 DIVQ(R2, R3); // 13 DIVQ(R2, R3); // 14 DIVQ(R2, R3); // 15 DIVQ(R2, R3); // 16 /* According to the Instruction Set Reference: To divide by a divisor > 0x7FFF, 1. prescale and perform divide to obtain quotient (Q) (done above), 2. multiply quotient by unscaled divisor (result M) 3. subtract the product from the divident to get an error (E = X - M) 4. if E < divisor (Y) subtract 1, if E > divisor (Y) add 1, else return quotient (Q) */ R3 = R2.L (Z); /* Q = X' / Y' */ R2 = R3; /* Preserve Q */ R2 *= R1; /* M = Q * Y */ R2 = R0 - R2; /* E = X - M */ R0 = R3; /* Copy Q into result reg */ /* Correction: If result of the multiply is negative, we overflowed and need to correct the result by subtracting 1 from the result.*/ R3 = 0xFFFF (Z); R2 = R2 >> 16; /* E >> 16 */ CC = R2 == R3; R3 = 1 ; R1 = R0 - R3; IF CC R0 = R1; RTS; ENDPROC(___udivsi3)