arch/blackfin/lib/muldi3.S

   1 /*
   2  * Copyright 2008 Analog Devices Inc.
   3  *
   4  * Licensed under the Clear BSD license or the GPL-2 (or later)
   5  */
   6
   7 .align 2
   8 .global ___muldi3;
   9 .type ___muldi3, STT_FUNC;
  10
  11 #ifdef CONFIG_ARITHMETIC_OPS_L1
  12 .section .l1.text
  13 #else
  14 .text
  15 #endif
  16
  17 /*
  18            R1:R0 * R3:R2
  19          = R1.h:R1.l:R0.h:R0.l * R3.h:R3.l:R2.h:R2.l
  20 [X]      = (R1.h * R3.h) * 2^96
  21 [X]        + (R1.h * R3.l + R1.l * R3.h) * 2^80
  22 [X]        + (R1.h * R2.h + R1.l * R3.l + R3.h * R0.h) * 2^64
  23 [T1]       + (R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h) * 2^48
  24 [T2]       + (R1.l * R2.l + R3.l * R0.l + R0.h * R2.h) * 2^32
  25 [T3]       + (R0.l * R2.h + R2.l * R0.h) * 2^16
  26 [T4]       + (R0.l * R2.l)
  27
  28         We can discard the first three lines marked "X" since we produce
  29         only a 64 bit result.  So, we need ten 16-bit multiplies.
  30
  31         Individual mul-acc results:
  32 [E1]     =  R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h
  33 [E2]     =  R1.l * R2.l + R3.l * R0.l + R0.h * R2.h
  34 [E3]     =  R0.l * R2.h + R2.l * R0.h
  35 [E4]     =  R0.l * R2.l
  36
  37         We also need to add high parts from lower-level results to higher ones:
  38         E[n]c = E[n] + (E[n+1]c >> 16), where E4c := E4
  39
  40         One interesting property is that all parts of the result that depend
  41         on the sign of the multiplication are discarded.  Those would be the
  42         multiplications involving R1.h and R3.h, but only the top 16 bit of
  43         the 32 bit result depend on the sign, and since R1.h and R3.h only
  44         occur in E1, the top half of these results is cut off.
  45         So, we can just use FU mode for all of the 16-bit multiplies, and
  46         ignore questions of when to use mixed mode.  */
  47
  48 ___muldi3:
  49         /* [SP] technically is part of the caller's frame, but we can
  50            use it as scratch space.  */
  51         A0 = R2.H * R1.L, A1 = R2.L * R1.H (FU) || R3 = [SP + 12];      /* E1 */
  52         A0 += R3.H * R0.L, A1 += R3.L * R0.H (FU) || [SP] = R4;         /* E1 */
  53         A0 += A1;                                                       /* E1 */
  54         R4 = A0.w;
  55         A0 = R0.l * R3.l (FU);                                          /* E2 */
  56         A0 += R2.l * R1.l (FU);                                         /* E2 */
  57
  58         A1 = R2.L * R0.L (FU);                                          /* E4 */
  59         R3 = A1.w;
  60         A1 = A1 >> 16;                                                  /* E3c */
  61         A0 += R2.H * R0.H, A1 += R2.L * R0.H (FU);                      /* E2, E3c */
  62         A1 += R0.L * R2.H (FU);                                         /* E3c */
  63         R0 = A1.w;
  64         A1 = A1 >> 16;                                                  /* E2c */
  65         A0 += A1;                                                       /* E2c */
  66         R1 = A0.w;
  67
  68         /* low(result) = low(E3c):low(E4) */
  69         R0 = PACK (R0.l, R3.l);
  70         /* high(result) = E2c + (E1 << 16) */
  71         R1.h = R1.h + R4.l (NS) || R4 = [SP];
  72         RTS;
  73
  74 .size ___muldi3, .-___muldi3