/*

 * Copyright (c) 2014, Red Hat Inc. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

#include <stdlib.h>

#include "decode_aarch64.hpp"

#include "immediate_aarch64.hpp"

// there are at most 2^13 possible logical immediate encodings

// however, some combinations of immr and imms are invalid

static const unsigned  LI_TABLE_SIZE = (1 << 13);

static int li_table_entry_count;

// for forward lookup we just use a direct array lookup

// and assume that the cient has supplied a valid encoding

// table[encoding] = immediate

static u_int64_t LITable[LI_TABLE_SIZE];

// for reverse lookup we need a sparse map so we store a table of

// immediate and encoding pairs sorted by immediate value

struct li_pair {

  u_int64_t immediate;

  u_int32_t encoding;

};

static struct li_pair InverseLITable[LI_TABLE_SIZE];

// comparator to sort entries in the inverse table

int compare_immediate_pair(const void *i1, const void *i2)

{

  struct li_pair *li1 = (struct li_pair *)i1;

  struct li_pair *li2 = (struct li_pair *)i2;

  if (li1->immediate < li2->immediate) {

    return -1;

  }

  if (li1->immediate > li2->immediate) {

    return 1;

  }

  return 0;

}

// helper functions used by expandLogicalImmediate

// for i = 1, ... N result<i-1> = 1 other bits are zero

static inline u_int64_t ones(int N)

{

  return (N == 64 ? (u_int64_t)-1UL : ((1UL << N) - 1));

}

// result<0> to val<N>

static inline u_int64_t pickbit(u_int64_t val, int N)

{

  return pickbits64(val, N, N);

}

// SPEC bits(M*N) Replicate(bits(M) x, integer N);

// this is just an educated guess

u_int64_t replicate(u_int64_t bits, int nbits, int count)

{

  u_int64_t result = 0;

  // nbits may be 64 in which case we want mask to be -1

  u_int64_t mask = ones(nbits);

  for (int i = 0; i < count ; i++) {

    result <<= nbits;

    result |= (bits & mask);

  }

  return result;

}

// this function writes the supplied bimm reference and returns a

// boolean to indicate success (1) or fail (0) because an illegal

// encoding must be treated as an UNALLOC instruction

// construct a 32 bit immediate value for a logical immediate operation

int expandLogicalImmediate(u_int32_t immN, u_int32_t immr,

                            u_int32_t imms, u_int64_t &bimm)

{

  int len;                  // ought to be <= 6

  u_int32_t levels;         // 6 bits

  u_int32_t tmask_and;      // 6 bits

  u_int32_t wmask_and;      // 6 bits

  u_int32_t tmask_or;       // 6 bits

  u_int32_t wmask_or;       // 6 bits

  u_int64_t imm64;          // 64 bits

  u_int64_t tmask, wmask;   // 64 bits

  u_int32_t S, R, diff;     // 6 bits?

  if (immN == 1) {

    len = 6; // looks like 7 given the spec above but this cannot be!

  } else {

    len = 0;

    u_int32_t val = (~imms & 0x3f);

    for (int i = 5; i > 0; i--) {

      if (val & (1 << i)) {

        len = i;

        break;

      }

    }

    if (len < 1) {

      return 0;

    }

    // for valid inputs leading 1s in immr must be less than leading

    // zeros in imms

    int len2 = 0;                   // ought to be < len

    u_int32_t val2 = (~immr & 0x3f);

    for (int i = 5; i > 0; i--) {

      if (!(val2 & (1 << i))) {

        len2 = i;

        break;

      }

    }

    if (len2 >= len) {

      return 0;

    }

  }

  levels = (1 << len) - 1;

  if ((imms & levels) == levels) {

    return 0;

  }

  S = imms & levels;

  R = immr & levels;

 // 6 bit arithmetic!

  diff = S - R;

  tmask_and = (diff | ~levels) & 0x3f;

  tmask_or = (diff & levels) & 0x3f;

  tmask = 0xffffffffffffffffULL;

  for (int i = 0; i < 6; i++) {

    int nbits = 1 << i;

    u_int64_t and_bit = pickbit(tmask_and, i);

    u_int64_t or_bit = pickbit(tmask_or, i);

    u_int64_t and_bits_sub = replicate(and_bit, 1, nbits);

    u_int64_t or_bits_sub = replicate(or_bit, 1, nbits);

    u_int64_t and_bits_top = (and_bits_sub << nbits) | ones(nbits);

    u_int64_t or_bits_top = (0 << nbits) | or_bits_sub;

    tmask = ((tmask

              & (replicate(and_bits_top, 2 * nbits, 32 / nbits)))

             | replicate(or_bits_top, 2 * nbits, 32 / nbits));

  }

  wmask_and = (immr | ~levels) & 0x3f;

  wmask_or = (immr & levels) & 0x3f;

  wmask = 0;

  for (int i = 0; i < 6; i++) {

    int nbits = 1 << i;

    u_int64_t and_bit = pickbit(wmask_and, i);

    u_int64_t or_bit = pickbit(wmask_or, i);

    u_int64_t and_bits_sub = replicate(and_bit, 1, nbits);

    u_int64_t or_bits_sub = replicate(or_bit, 1, nbits);

    u_int64_t and_bits_top = (ones(nbits) << nbits) | and_bits_sub;

    u_int64_t or_bits_top = (or_bits_sub << nbits) | 0;

    wmask = ((wmask

              & (replicate(and_bits_top, 2 * nbits, 32 / nbits)))

             | replicate(or_bits_top, 2 * nbits, 32 / nbits));

  }

  if (diff & (1U << 6)) {

    imm64 = tmask & wmask;

  } else {

    imm64 = tmask | wmask;

  }

  bimm = imm64;

  return 1;

}

// constructor to initialise the lookup tables

static void initLITables() __attribute__ ((constructor));

static void initLITables()

{

  li_table_entry_count = 0;

  for (unsigned index = 0; index < LI_TABLE_SIZE; index++) {

    u_int32_t N = uimm(index, 12, 12);

    u_int32_t immr = uimm(index, 11, 6);

    u_int32_t imms = uimm(index, 5, 0);

    if (expandLogicalImmediate(N, immr, imms, LITable[index])) {

      InverseLITable[li_table_entry_count].immediate = LITable[index];

      InverseLITable[li_table_entry_count].encoding = index;

      li_table_entry_count++;

    }

  }

  // now sort the inverse table

  qsort(InverseLITable, li_table_entry_count,

        sizeof(InverseLITable[0]), compare_immediate_pair);

}

// public APIs provided for logical immediate lookup and reverse lookup

u_int64_t logical_immediate_for_encoding(u_int32_t encoding)

{

  return LITable[encoding];

}

u_int32_t encoding_for_logical_immediate(u_int64_t immediate)

{

  struct li_pair pair;

  struct li_pair *result;

  pair.immediate = immediate;

  result = (struct li_pair *)

    bsearch(&pair, InverseLITable, li_table_entry_count,

            sizeof(InverseLITable[0]), compare_immediate_pair);

  if (result) {

    return result->encoding;

  }

  return 0xffffffff;

}

// floating point immediates are encoded in 8 bits

// fpimm[7] = sign bit

// fpimm[6:4] = signed exponent

// fpimm[3:0] = fraction (assuming leading 1)

// i.e. F = s * 1.f * 2^(e - b)

u_int64_t fp_immediate_for_encoding(u_int32_t imm8, int is_dp)

{

  union {

    float fpval;

    double dpval;

    u_int64_t val;

  };

  u_int32_t s, e, f;

  s = (imm8 >> 7 ) & 0x1;

  e = (imm8 >> 4) & 0x7;

  f = imm8 & 0xf;

  // the fp value is s * n/16 * 2r where n is 16+e

  fpval = (16.0 + f) / 16.0;

  // n.b. exponent is signed

  if (e < 4) {

    int epos = e;

    for (int i = 0; i <= epos; i++) {

      fpval *= 2.0;

    }

  } else {

    int eneg = 7 - e;

    for (int i = 0; i < eneg; i++) {

      fpval /= 2.0;

    }

  }

  if (s) {

    fpval = -fpval;

  }

  if (is_dp) {

    dpval = (double)fpval;

  }

  return val;

}

u_int32_t encoding_for_fp_immediate(float immediate)

{

  // given a float which is of the form

  //

  //     s * n/16 * 2r

  //

  // where n is 16+f and imm1:s, imm4:f, simm3:r

  // return the imm8 result [s:r:f]

  //

  union {

    float fpval;

    u_int32_t val;

  };

  fpval = immediate;

  u_int32_t s, r, f, res;

  // sign bit is 31

  s = (val >> 31) & 0x1;

  // exponent is bits 30-23 but we only want the bottom 3 bits

  // strictly we ought to check that the bits bits 30-25 are

  // either all 1s or all 0s

  r = (val >> 23) & 0x7;

  // fraction is bits 22-0

  f = (val >> 19) & 0xf;

  res = (s << 7) | (r << 4) | f;

  return res;

}