| /* |
| * Copyright 2004-2009 Analog Devices Inc. |
| * |
| * Licensed under the ADI BSD license or the GPL-2 (or later) |
| */ |
| |
| #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; |
| |
| ENDPROC(___udivsi3) |
