arch/blackfin/lib/divsi3.S

   1 /*
   2  * Copyright 2004-2009 Analog Devices Inc.
   3  *
   4  * Licensed under the Clear BSD license or the GPL-2 (or later)
   5  *
   6  * 16 / 32 bit signed division.
   7  *                 Special cases :
   8  *                      1)  If(numerator == 0)
   9  *                             return 0
  10  *                      2)  If(denominator ==0)
  11  *                             return positive max = 0x7fffffff
  12  *                      3)  If(numerator == denominator)
  13  *                             return 1
  14  *                      4)  If(denominator ==1)
  15  *                             return numerator
  16  *                      5)  If(denominator == -1)
  17  *                             return -numerator
  18  *
  19  *                 Operand         : R0 - Numerator   (i)
  20  *                                   R1 - Denominator (i)
  21  *                                   R0 - Quotient    (o)
  22  *                 Registers Used : R2-R7,P0-P2
  23  *
  24  */
  25
  26 .global   ___divsi3;
  27 .type ___divsi3, STT_FUNC;
  28
  29 #ifdef CONFIG_ARITHMETIC_OPS_L1
  30 .section .l1.text
  31 #else
  32 .text
  33 #endif
  34
  35 .align 2;
  36 ___divsi3 :
  37
  38
  39   R3 = R0 ^ R1;
  40   R0 = ABS R0;
  41
  42   CC = V;
  43
  44   r3 = rot r3 by -1;
  45   r1 = abs r1;      /* now both positive, r3.30 means "negate result",
  46                     ** r3.31 means overflow, add one to result
  47                     */
  48   cc = r0 < r1;
  49   if cc jump .Lret_zero;
  50   r2 = r1 >> 15;
  51   cc = r2;
  52   if cc jump .Lidents;
  53   r2 = r1 << 16;
  54   cc = r2 <= r0;
  55   if cc jump .Lidents;
  56
  57   DIVS(R0, R1);
  58   DIVQ(R0, R1);
  59   DIVQ(R0, R1);
  60   DIVQ(R0, R1);
  61   DIVQ(R0, R1);
  62   DIVQ(R0, R1);
  63   DIVQ(R0, R1);
  64   DIVQ(R0, R1);
  65   DIVQ(R0, R1);
  66   DIVQ(R0, R1);
  67   DIVQ(R0, R1);
  68   DIVQ(R0, R1);
  69   DIVQ(R0, R1);
  70   DIVQ(R0, R1);
  71   DIVQ(R0, R1);
  72   DIVQ(R0, R1);
  73   DIVQ(R0, R1);
  74
  75   R0 = R0.L (Z);
  76   r1 = r3 >> 31;    /* add overflow issue back in */
  77   r0 = r0 + r1;
  78   r1 = -r0;
  79   cc = bittst(r3, 30);
  80   if cc r0 = r1;
  81   RTS;
  82
  83 /* Can't use the primitives. Test common identities.
  84 ** If the identity is true, return the value in R2.
  85 */
  86
  87 .Lidents:
  88   CC = R1 == 0;                   /* check for divide by zero */
  89   IF CC JUMP .Lident_return;
  90
  91   CC = R0 == 0;                   /* check for division of zero */
  92   IF CC JUMP .Lzero_return;
  93
  94   CC = R0 == R1;                  /* check for identical operands */
  95   IF CC JUMP .Lident_return;
  96
  97   CC = R1 == 1;                   /* check for divide by 1 */
  98   IF CC JUMP .Lident_return;
  99
 100   R2.L = ONES R1;
 101   R2 = R2.L (Z);
 102   CC = R2 == 1;
 103   IF CC JUMP .Lpower_of_two;
 104
 105   /* Identities haven't helped either.
 106   ** Perform the full division process.
 107   */
 108
 109   P1 = 31;                        /* Set loop counter   */
 110
 111   [--SP] = (R7:5);                /* Push registers R5-R7 */
 112   R2 = -R1;
 113   [--SP] = R2;
 114   R2 = R0 << 1;                   /* R2 lsw of dividend  */
 115   R6 = R0 ^ R1;                   /* Get sign */
 116   R5 = R6 >> 31;                  /* Shift sign to LSB */
 117
 118   R0 = 0 ;                        /* Clear msw partial remainder */
 119   R2 = R2 | R5;                   /* Shift quotient bit */
 120   R6 = R0 ^ R1;                   /* Get new quotient bit */
 121
 122   LSETUP(.Llst,.Llend)  LC0 = P1;   /* Setup loop */
 123 .Llst:   R7 = R2 >> 31;            /* record copy of carry from R2 */
 124         R2 = R2 << 1;             /* Shift 64 bit dividend up by 1 bit */
 125         R0 = R0 << 1 || R5 = [SP];
 126         R0 = R0 | R7;             /* and add carry */
 127         CC = R6 < 0;              /* Check quotient(AQ) */
 128                                   /* we might be subtracting divisor (AQ==0) */
 129         IF CC R5 = R1;            /* or we might be adding divisor  (AQ==1)*/
 130         R0 = R0 + R5;             /* do add or subtract, as indicated by AQ */
 131         R6 = R0 ^ R1;             /* Generate next quotient bit */
 132         R5 = R6 >> 31;
 133                                   /* Assume AQ==1, shift in zero */
 134         BITTGL(R5,0);             /* tweak AQ to be what we want to shift in */
 135 .Llend:  R2 = R2 + R5;             /* and then set shifted-in value to
 136                                   ** tweaked AQ.
 137                                   */
 138   r1 = r3 >> 31;
 139   r2 = r2 + r1;
 140   cc = bittst(r3,30);
 141   r0 = -r2;
 142   if !cc r0 = r2;
 143   SP += 4;
 144   (R7:5)= [SP++];                 /* Pop registers R6-R7 */
 145   RTS;
 146
 147 .Lident_return:
 148   CC = R1 == 0;                   /* check for divide by zero  => 0x7fffffff */
 149   R2 = -1 (X);
 150   R2 >>= 1;
 151   IF CC JUMP .Ltrue_ident_return;
 152
 153   CC = R0 == R1;                  /* check for identical operands => 1 */
 154   R2 = 1 (Z);
 155   IF CC JUMP .Ltrue_ident_return;
 156
 157   R2 = R0;                        /* assume divide by 1 => numerator */
 158   /*FALLTHRU*/
 159
 160 .Ltrue_ident_return:
 161   R0 = R2;                        /* Return an identity value */
 162   R2 = -R2;
 163   CC = bittst(R3,30);
 164   IF CC R0 = R2;
 165 .Lzero_return:
 166   RTS;                            /* ...including zero */
 167
 168 .Lpower_of_two:
 169   /* Y has a single bit set, which means it's a power of two.
 170   ** That means we can perform the division just by shifting
 171   ** X to the right the appropriate number of bits
 172   */
 173
 174   /* signbits returns the number of sign bits, minus one.
 175   ** 1=>30, 2=>29, ..., 0x40000000=>0. Which means we need
 176   ** to shift right n-signbits spaces. It also means 0x80000000
 177   ** is a special case, because that *also* gives a signbits of 0
 178   */
 179
 180   R2 = R0 >> 31;
 181   CC = R1 < 0;
 182   IF CC JUMP .Ltrue_ident_return;
 183
 184   R1.l = SIGNBITS R1;
 185   R1 = R1.L (Z);
 186   R1 += -30;
 187   R0 = LSHIFT R0 by R1.L;
 188   r1 = r3 >> 31;
 189   r0 = r0 + r1;
 190   R2 = -R0;                       // negate result if necessary
 191   CC = bittst(R3,30);
 192   IF CC R0 = R2;
 193   RTS;
 194
 195 .Lret_zero:
 196   R0 = 0;
 197   RTS;
 198
 199 .size ___divsi3, .-___divsi3