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Diffstat (limited to 'arch/blackfin/lib/udivsi3.S')
| -rw-r--r-- | arch/blackfin/lib/udivsi3.S | 298 |
1 files changed, 298 insertions, 0 deletions
diff --git a/arch/blackfin/lib/udivsi3.S b/arch/blackfin/lib/udivsi3.S new file mode 100644 index 000000000000..d39a12916259 --- /dev/null +++ b/arch/blackfin/lib/udivsi3.S @@ -0,0 +1,298 @@ +/* + * File: arch/blackfin/lib/udivsi3.S + * Based on: + * Author: + * + * Created: + * Description: + * + * Modified: + * Copyright 2004-2006 Analog Devices Inc. + * + * Bugs: Enter bugs at http://blackfin.uclinux.org/ + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see the file COPYING, or write + * to the Free Software Foundation, Inc., + * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include <linux/linkage.h> + +#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; |