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math.c

/*
 * arch/sparc/math-emu/math.c
 *
 * Copyright (C) 1998 Peter Maydell (pmaydell@chiark.greenend.org.uk)
 * Copyright (C) 1997, 1999 Jakub Jelinek (jj@ultra.linux.cz)
 * Copyright (C) 1999 David S. Miller (davem@redhat.com)
 *
 * This is a good place to start if you're trying to understand the
 * emulation code, because it's pretty simple. What we do is
 * essentially analyse the instruction to work out what the operation
 * is and which registers are involved. We then execute the appropriate
 * FXXXX function. [The floating point queue introduces a minor wrinkle;
 * see below...]
 * The fxxxxx.c files each emulate a single insn. They look relatively
 * simple because the complexity is hidden away in an unholy tangle
 * of preprocessor macros.
 *
 * The first layer of macros is single.h, double.h, quad.h. Generally
 * these files define macros for working with floating point numbers
 * of the three IEEE formats. FP_ADD_D(R,A,B) is for adding doubles,
 * for instance. These macros are usually defined as calls to more
 * generic macros (in this case _FP_ADD(D,2,R,X,Y) where the number
 * of machine words required to store the given IEEE format is passed
 * as a parameter. [double.h and co check the number of bits in a word
 * and define FP_ADD_D & co appropriately].
 * The generic macros are defined in op-common.h. This is where all
 * the grotty stuff like handling NaNs is coded. To handle the possible
 * word sizes macros in op-common.h use macros like _FP_FRAC_SLL_##wc()
 * where wc is the 'number of machine words' parameter (here 2).
 * These are defined in the third layer of macros: op-1.h, op-2.h
 * and op-4.h. These handle operations on floating point numbers composed
 * of 1,2 and 4 machine words respectively. [For example, on sparc64
 * doubles are one machine word so macros in double.h eventually use
 * constructs in op-1.h, but on sparc32 they use op-2.h definitions.]
 * soft-fp.h is on the same level as op-common.h, and defines some
 * macros which are independent of both word size and FP format.
 * Finally, sfp-machine.h is the machine dependent part of the
 * code: it defines the word size and what type a word is. It also
 * defines how _FP_MUL_MEAT_t() maps to _FP_MUL_MEAT_n_* : op-n.h
 * provide several possible flavours of multiply algorithm, most
 * of which require that you supply some form of asm or C primitive to
 * do the actual multiply. (such asm primitives should be defined
 * in sfp-machine.h too). udivmodti4.c is the same sort of thing.
 *
 * There may be some errors here because I'm working from a
 * SPARC architecture manual V9, and what I really want is V8...
 * Also, the insns which can generate exceptions seem to be a
 * greater subset of the FPops than for V9 (for example, FCMPED
 * has to be emulated on V8). So I think I'm going to have
 * to emulate them all just to be on the safe side...
 *
 * Emulation routines originate from soft-fp package, which is
 * part of glibc and has appropriate copyrights in it (allegedly).
 *
 * NB: on sparc int == long == 4 bytes, long long == 8 bytes.
 * Most bits of the kernel seem to go for long rather than int,
 * so we follow that practice...
 */

/* TODO:
 * fpsave() saves the FP queue but fpload() doesn't reload it.
 * Therefore when we context switch or change FPU ownership
 * we have to check to see if the queue had anything in it and
 * emulate it if it did. This is going to be a pain.
 */

#include <linux/types.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <asm/uaccess.h>

#include "sfp-util.h"
#include <math-emu/soft-fp.h>
#include <math-emu/single.h>
#include <math-emu/double.h>
#include <math-emu/quad.h>

#define FLOATFUNC(x) extern int x(void *,void *,void *)

/* The Vn labels indicate what version of the SPARC architecture gas thinks
 * each insn is. This is from the binutils source :->
 */
/* quadword instructions */
#define FSQRTQ    0x02b       /* v8 */
#define FADDQ     0x043       /* v8 */
#define FSUBQ     0x047       /* v8 */
#define FMULQ     0x04b       /* v8 */
#define FDIVQ     0x04f       /* v8 */
#define FDMULQ    0x06e       /* v8 */
#define FQTOS     0x0c7       /* v8 */
#define FQTOD     0x0cb       /* v8 */
#define FITOQ     0x0cc       /* v8 */
#define FSTOQ     0x0cd       /* v8 */
#define FDTOQ     0x0ce       /* v8 */
#define FQTOI     0x0d3       /* v8 */
#define FCMPQ     0x053       /* v8 */
#define FCMPEQ    0x057       /* v8 */
/* single/double instructions (subnormal): should all work */
#define FSQRTS    0x029       /* v7 */
#define FSQRTD    0x02a       /* v7 */
#define FADDS     0x041       /* v6 */
#define FADDD     0x042       /* v6 */
#define FSUBS     0x045       /* v6 */
#define FSUBD     0x046       /* v6 */
#define FMULS     0x049       /* v6 */
#define FMULD     0x04a       /* v6 */
#define FDIVS     0x04d       /* v6 */
#define FDIVD     0x04e       /* v6 */
#define FSMULD    0x069       /* v6 */
#define FDTOS     0x0c6       /* v6 */
#define FSTOD     0x0c9       /* v6 */
#define FSTOI     0x0d1       /* v6 */
#define FDTOI     0x0d2       /* v6 */
#define FABSS     0x009       /* v6 */
#define FCMPS     0x051       /* v6 */
#define FCMPES    0x055       /* v6 */
#define FCMPD     0x052       /* v6 */
#define FCMPED    0x056       /* v6 */
#define FMOVS     0x001       /* v6 */
#define FNEGS     0x005       /* v6 */
#define FITOS     0x0c4       /* v6 */
#define FITOD     0x0c8       /* v6 */

#define FSR_TEM_SHIFT   23UL
#define FSR_TEM_MASK    (0x1fUL << FSR_TEM_SHIFT)
#define FSR_AEXC_SHIFT  5UL
#define FSR_AEXC_MASK   (0x1fUL << FSR_AEXC_SHIFT)
#define FSR_CEXC_SHIFT  0UL
#define FSR_CEXC_MASK   (0x1fUL << FSR_CEXC_SHIFT)

static int do_one_mathemu(u32 insn, unsigned long *fsr, unsigned long *fregs);

/* Unlike the Sparc64 version (which has a struct fpustate), we
 * pass the taskstruct corresponding to the task which currently owns the
 * FPU. This is partly because we don't have the fpustate struct and
 * partly because the task owning the FPU isn't always current (as is
 * the case for the Sparc64 port). This is probably SMP-related...
 * This function returns 1 if all queued insns were emulated successfully.
 * The test for unimplemented FPop in kernel mode has been moved into
 * kernel/traps.c for simplicity.
 */
int do_mathemu(struct pt_regs *regs, struct task_struct *fpt)
{
      /* regs->pc isn't necessarily the PC at which the offending insn is sitting.
       * The FPU maintains a queue of FPops which cause traps.
       * When it hits an instruction that requires that the trapped op succeeded
       * (usually because it reads a reg. that the trapped op wrote) then it
       * causes this exception. We need to emulate all the insns on the queue
       * and then allow the op to proceed.
       * This code should also handle the case where the trap was precise,
       * in which case the queue length is zero and regs->pc points at the
       * single FPop to be emulated. (this case is untested, though :->)
       * You'll need this case if you want to be able to emulate all FPops
       * because the FPU either doesn't exist or has been software-disabled.
       * [The UltraSPARC makes FP a precise trap; this isn't as stupid as it
       * might sound because the Ultra does funky things with a superscalar
       * architecture.]
       */

      /* You wouldn't believe how often I typed 'ftp' when I meant 'fpt' :-> */

      int i;
      int retcode = 0;                               /* assume all succeed */
      unsigned long insn;

#ifdef DEBUG_MATHEMU
      printk("In do_mathemu()... pc is %08lx\n", regs->pc);
      printk("fpqdepth is %ld\n", fpt->thread.fpqdepth);
      for (i = 0; i < fpt->thread.fpqdepth; i++)
            printk("%d: %08lx at %08lx\n", i, fpt->thread.fpqueue[i].insn,
                   (unsigned long)fpt->thread.fpqueue[i].insn_addr);
#endif

      if (fpt->thread.fpqdepth == 0) {                   /* no queue, guilty insn is at regs->pc */
#ifdef DEBUG_MATHEMU
            printk("precise trap at %08lx\n", regs->pc);
#endif
            if (!get_user(insn, (u32 __user *) regs->pc)) {
                  retcode = do_one_mathemu(insn, &fpt->thread.fsr, fpt->thread.float_regs);
                  if (retcode) {
                        /* in this case we need to fix up PC & nPC */
                        regs->pc = regs->npc;
                        regs->npc += 4;
                  }
            }
            return retcode;
      }

      /* Normal case: need to empty the queue... */
      for (i = 0; i < fpt->thread.fpqdepth; i++) {
            retcode = do_one_mathemu(fpt->thread.fpqueue[i].insn, &(fpt->thread.fsr), fpt->thread.float_regs);
            if (!retcode)                               /* insn failed, no point doing any more */
                  break;
      }
      /* Now empty the queue and clear the queue_not_empty flag */
      if (retcode)
            fpt->thread.fsr &= ~(0x3000 | FSR_CEXC_MASK);
      else
            fpt->thread.fsr &= ~0x3000;
      fpt->thread.fpqdepth = 0;

      return retcode;
}

/* All routines returning an exception to raise should detect
 * such exceptions _before_ rounding to be consistent with
 * the behavior of the hardware in the implemented cases
 * (and thus with the recommendations in the V9 architecture
 * manual).
 *
 * We return 0 if a SIGFPE should be sent, 1 otherwise.
 */
static inline int record_exception(unsigned long *pfsr, int eflag)
{
      unsigned long fsr = *pfsr;
      int would_trap;

      /* Determine if this exception would have generated a trap. */
      would_trap = (fsr & ((long)eflag << FSR_TEM_SHIFT)) != 0UL;

      /* If trapping, we only want to signal one bit. */
      if (would_trap != 0) {
            eflag &= ((fsr & FSR_TEM_MASK) >> FSR_TEM_SHIFT);
            if ((eflag & (eflag - 1)) != 0) {
                  if (eflag & FP_EX_INVALID)
                        eflag = FP_EX_INVALID;
                  else if (eflag & FP_EX_OVERFLOW)
                        eflag = FP_EX_OVERFLOW;
                  else if (eflag & FP_EX_UNDERFLOW)
                        eflag = FP_EX_UNDERFLOW;
                  else if (eflag & FP_EX_DIVZERO)
                        eflag = FP_EX_DIVZERO;
                  else if (eflag & FP_EX_INEXACT)
                        eflag = FP_EX_INEXACT;
            }
      }

      /* Set CEXC, here is the rule:
       *
       *    In general all FPU ops will set one and only one
       *    bit in the CEXC field, this is always the case
       *    when the IEEE exception trap is enabled in TEM.
       */
      fsr &= ~(FSR_CEXC_MASK);
      fsr |= ((long)eflag << FSR_CEXC_SHIFT);

      /* Set the AEXC field, rule is:
       *
       *    If a trap would not be generated, the
       *    CEXC just generated is OR'd into the
       *    existing value of AEXC.
       */
      if (would_trap == 0)
            fsr |= ((long)eflag << FSR_AEXC_SHIFT);

      /* If trapping, indicate fault trap type IEEE. */
      if (would_trap != 0)
            fsr |= (1UL << 14);

      *pfsr = fsr;

      return (would_trap ? 0 : 1);
}

typedef union {
      u32 s;
      u64 d;
      u64 q[2];
} *argp;

static int do_one_mathemu(u32 insn, unsigned long *pfsr, unsigned long *fregs)
{
      /* Emulate the given insn, updating fsr and fregs appropriately. */
      int type = 0;
      /* r is rd, b is rs2 and a is rs1. The *u arg tells
         whether the argument should be packed/unpacked (0 - do not unpack/pack, 1 - unpack/pack)
         non-u args tells the size of the argument (0 - no argument, 1 - single, 2 - double, 3 - quad */
#define TYPE(dummy, r, ru, b, bu, a, au) type = (au << 2) | (a << 0) | (bu << 5) | (b << 3) | (ru << 8) | (r << 6)
      int freg;
      argp rs1 = NULL, rs2 = NULL, rd = NULL;
      FP_DECL_EX;
      FP_DECL_S(SA); FP_DECL_S(SB); FP_DECL_S(SR);
      FP_DECL_D(DA); FP_DECL_D(DB); FP_DECL_D(DR);
      FP_DECL_Q(QA); FP_DECL_Q(QB); FP_DECL_Q(QR);
      int IR;
      long fsr;

#ifdef DEBUG_MATHEMU
      printk("In do_mathemu(), emulating %08lx\n", insn);
#endif

      if ((insn & 0xc1f80000) == 0x81a00000)    /* FPOP1 */ {
            switch ((insn >> 5) & 0x1ff) {
            case FSQRTQ: TYPE(3,3,1,3,1,0,0); break;
            case FADDQ:
            case FSUBQ:
            case FMULQ:
            case FDIVQ: TYPE(3,3,1,3,1,3,1); break;
            case FDMULQ: TYPE(3,3,1,2,1,2,1); break;
            case FQTOS: TYPE(3,1,1,3,1,0,0); break;
            case FQTOD: TYPE(3,2,1,3,1,0,0); break;
            case FITOQ: TYPE(3,3,1,1,0,0,0); break;
            case FSTOQ: TYPE(3,3,1,1,1,0,0); break;
            case FDTOQ: TYPE(3,3,1,2,1,0,0); break;
            case FQTOI: TYPE(3,1,0,3,1,0,0); break;
            case FSQRTS: TYPE(2,1,1,1,1,0,0); break;
            case FSQRTD: TYPE(2,2,1,2,1,0,0); break;
            case FADDD:
            case FSUBD:
            case FMULD:
            case FDIVD: TYPE(2,2,1,2,1,2,1); break;
            case FADDS:
            case FSUBS:
            case FMULS:
            case FDIVS: TYPE(2,1,1,1,1,1,1); break;
            case FSMULD: TYPE(2,2,1,1,1,1,1); break;
            case FDTOS: TYPE(2,1,1,2,1,0,0); break;
            case FSTOD: TYPE(2,2,1,1,1,0,0); break;
            case FSTOI: TYPE(2,1,0,1,1,0,0); break;
            case FDTOI: TYPE(2,1,0,2,1,0,0); break;
            case FITOS: TYPE(2,1,1,1,0,0,0); break;
            case FITOD: TYPE(2,2,1,1,0,0,0); break;
            case FMOVS:
            case FABSS:
            case FNEGS: TYPE(2,1,0,1,0,0,0); break;
            }
      } else if ((insn & 0xc1f80000) == 0x81a80000)   /* FPOP2 */ {
            switch ((insn >> 5) & 0x1ff) {
            case FCMPS: TYPE(3,0,0,1,1,1,1); break;
            case FCMPES: TYPE(3,0,0,1,1,1,1); break;
            case FCMPD: TYPE(3,0,0,2,1,2,1); break;
            case FCMPED: TYPE(3,0,0,2,1,2,1); break;
            case FCMPQ: TYPE(3,0,0,3,1,3,1); break;
            case FCMPEQ: TYPE(3,0,0,3,1,3,1); break;
            }
      }

      if (!type) {      /* oops, didn't recognise that FPop */
#ifdef DEBUG_MATHEMU
            printk("attempt to emulate unrecognised FPop!\n");
#endif
            return 0;
      }

      /* Decode the registers to be used */
      freg = (*pfsr >> 14) & 0xf;

      *pfsr &= ~0x1c000;                        /* clear the traptype bits */
      
      freg = ((insn >> 14) & 0x1f);
      switch (type & 0x3) {                     /* is rs1 single, double or quad? */
      case 3:
            if (freg & 3) {                     /* quadwords must have bits 4&5 of the */
                                          /* encoded reg. number set to zero. */
                  *pfsr |= (6 << 14);
                  return 0;               /* simulate invalid_fp_register exception */
            }
      /* fall through */
      case 2:
            if (freg & 1) {                     /* doublewords must have bit 5 zeroed */
                  *pfsr |= (6 << 14);
                  return 0;
            }
      }
      rs1 = (argp)&fregs[freg];
      switch (type & 0x7) {
      case 7: FP_UNPACK_QP (QA, rs1); break;
      case 6: FP_UNPACK_DP (DA, rs1); break;
      case 5: FP_UNPACK_SP (SA, rs1); break;
      }
      freg = (insn & 0x1f);
      switch ((type >> 3) & 0x3) {              /* same again for rs2 */
      case 3:
            if (freg & 3) {                     /* quadwords must have bits 4&5 of the */
                                          /* encoded reg. number set to zero. */
                  *pfsr |= (6 << 14);
                  return 0;               /* simulate invalid_fp_register exception */
            }
      /* fall through */
      case 2:
            if (freg & 1) {                     /* doublewords must have bit 5 zeroed */
                  *pfsr |= (6 << 14);
                  return 0;
            }
      }
      rs2 = (argp)&fregs[freg];
      switch ((type >> 3) & 0x7) {
      case 7: FP_UNPACK_QP (QB, rs2); break;
      case 6: FP_UNPACK_DP (DB, rs2); break;
      case 5: FP_UNPACK_SP (SB, rs2); break;
      }
      freg = ((insn >> 25) & 0x1f);
      switch ((type >> 6) & 0x3) {              /* and finally rd. This one's a bit different */
      case 0:                                   /* dest is fcc. (this must be FCMPQ or FCMPEQ) */
            if (freg) {                   /* V8 has only one set of condition codes, so */
                                          /* anything but 0 in the rd field is an error */
                  *pfsr |= (6 << 14);           /* (should probably flag as invalid opcode */
                  return 0;               /* but SIGFPE will do :-> ) */
            }
            break;
      case 3:
            if (freg & 3) {                     /* quadwords must have bits 4&5 of the */
                                          /* encoded reg. number set to zero. */
                  *pfsr |= (6 << 14);
                  return 0;               /* simulate invalid_fp_register exception */
            }
      /* fall through */
      case 2:
            if (freg & 1) {                     /* doublewords must have bit 5 zeroed */
                  *pfsr |= (6 << 14);
                  return 0;
            }
      /* fall through */
      case 1:
            rd = (void *)&fregs[freg];
            break;
      }
#ifdef DEBUG_MATHEMU
      printk("executing insn...\n");
#endif
      /* do the Right Thing */
      switch ((insn >> 5) & 0x1ff) {
      /* + */
      case FADDS: FP_ADD_S (SR, SA, SB); break;
      case FADDD: FP_ADD_D (DR, DA, DB); break;
      case FADDQ: FP_ADD_Q (QR, QA, QB); break;
      /* - */
      case FSUBS: FP_SUB_S (SR, SA, SB); break;
      case FSUBD: FP_SUB_D (DR, DA, DB); break;
      case FSUBQ: FP_SUB_Q (QR, QA, QB); break;
      /* * */
      case FMULS: FP_MUL_S (SR, SA, SB); break;
      case FSMULD: FP_CONV (D, S, 2, 1, DA, SA);
                 FP_CONV (D, S, 2, 1, DB, SB);
      case FMULD: FP_MUL_D (DR, DA, DB); break;
      case FDMULQ: FP_CONV (Q, D, 4, 2, QA, DA);
                 FP_CONV (Q, D, 4, 2, QB, DB);
      case FMULQ: FP_MUL_Q (QR, QA, QB); break;
      /* / */
      case FDIVS: FP_DIV_S (SR, SA, SB); break;
      case FDIVD: FP_DIV_D (DR, DA, DB); break;
      case FDIVQ: FP_DIV_Q (QR, QA, QB); break;
      /* sqrt */
      case FSQRTS: FP_SQRT_S (SR, SB); break;
      case FSQRTD: FP_SQRT_D (DR, DB); break;
      case FSQRTQ: FP_SQRT_Q (QR, QB); break;
      /* mov */
      case FMOVS: rd->s = rs2->s; break;
      case FABSS: rd->s = rs2->s & 0x7fffffff; break;
      case FNEGS: rd->s = rs2->s ^ 0x80000000; break;
      /* float to int */
      case FSTOI: FP_TO_INT_S (IR, SB, 32, 1); break;
      case FDTOI: FP_TO_INT_D (IR, DB, 32, 1); break;
      case FQTOI: FP_TO_INT_Q (IR, QB, 32, 1); break;
      /* int to float */
      case FITOS: IR = rs2->s; FP_FROM_INT_S (SR, IR, 32, int); break;
      case FITOD: IR = rs2->s; FP_FROM_INT_D (DR, IR, 32, int); break;
      case FITOQ: IR = rs2->s; FP_FROM_INT_Q (QR, IR, 32, int); break;
      /* float to float */
      case FSTOD: FP_CONV (D, S, 2, 1, DR, SB); break;
      case FSTOQ: FP_CONV (Q, S, 4, 1, QR, SB); break;
      case FDTOQ: FP_CONV (Q, D, 4, 2, QR, DB); break;
      case FDTOS: FP_CONV (S, D, 1, 2, SR, DB); break;
      case FQTOS: FP_CONV (S, Q, 1, 4, SR, QB); break;
      case FQTOD: FP_CONV (D, Q, 2, 4, DR, QB); break;
      /* comparison */
      case FCMPS:
      case FCMPES:
            FP_CMP_S(IR, SB, SA, 3);
            if (IR == 3 &&
                (((insn >> 5) & 0x1ff) == FCMPES ||
                 FP_ISSIGNAN_S(SA) ||
                 FP_ISSIGNAN_S(SB)))
                  FP_SET_EXCEPTION (FP_EX_INVALID);
            break;
      case FCMPD:
      case FCMPED:
            FP_CMP_D(IR, DB, DA, 3);
            if (IR == 3 &&
                (((insn >> 5) & 0x1ff) == FCMPED ||
                 FP_ISSIGNAN_D(DA) ||
                 FP_ISSIGNAN_D(DB)))
                  FP_SET_EXCEPTION (FP_EX_INVALID);
            break;
      case FCMPQ:
      case FCMPEQ:
            FP_CMP_Q(IR, QB, QA, 3);
            if (IR == 3 &&
                (((insn >> 5) & 0x1ff) == FCMPEQ ||
                 FP_ISSIGNAN_Q(QA) ||
                 FP_ISSIGNAN_Q(QB)))
                  FP_SET_EXCEPTION (FP_EX_INVALID);
      }
      if (!FP_INHIBIT_RESULTS) {
            switch ((type >> 6) & 0x7) {
            case 0: fsr = *pfsr;
                  if (IR == -1) IR = 2;
                  /* fcc is always fcc0 */
                  fsr &= ~0xc00; fsr |= (IR << 10); break;
                  *pfsr = fsr;
                  break;
            case 1: rd->s = IR; break;
            case 5: FP_PACK_SP (rd, SR); break;
            case 6: FP_PACK_DP (rd, DR); break;
            case 7: FP_PACK_QP (rd, QR); break;
            }
      }
      if (_fex == 0)
            return 1;                     /* success! */
      return record_exception(pfsr, _fex);
}

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