const1.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // constant conversions
     6  
     7  package const1
     8  
     9  import "math"
    10  
    11  const(
    12  	mi = ^int(0)
    13  	mu = ^uint(0)
    14  	mp = ^uintptr(0)
    15  
    16  	logSizeofInt     = uint(mi>>8&1 + mi>>16&1 + mi>>32&1)
    17  	logSizeofUint    = uint(mu>>8&1 + mu>>16&1 + mu>>32&1)
    18  	logSizeofUintptr = uint(mp>>8&1 + mp>>16&1 + mp>>32&1)
    19  )
    20  
    21  const (
    22  	minInt8 = -1<<(8<<iota - 1)
    23  	minInt16
    24  	minInt32
    25  	minInt64
    26  	minInt = -1<<(8<<logSizeofInt - 1)
    27  )
    28  
    29  const (
    30  	maxInt8 = 1<<(8<<iota - 1) - 1
    31  	maxInt16
    32  	maxInt32
    33  	maxInt64
    34  	maxInt = 1<<(8<<logSizeofInt - 1) - 1
    35  )
    36  
    37  const (
    38  	maxUint8 = 1<<(8<<iota) - 1
    39  	maxUint16
    40  	maxUint32
    41  	maxUint64
    42  	maxUint    = 1<<(8<<logSizeofUint) - 1
    43  	maxUintptr = 1<<(8<<logSizeofUintptr) - 1
    44  )
    45  
    46  const (
    47  	smallestFloat32 = 1.0 / (1<<(127 - 1 + 23))
    48  	// TODO(gri) The compiler limits integers to 512 bit and thus
    49  	//           we cannot compute the value (1<<(1023 - 1 + 52))
    50  	//           without overflow. For now we match the compiler.
    51  	//           See also issue #44057.
    52  	// smallestFloat64 = 1.0 / (1<<(1023 - 1 + 52))
    53  	smallestFloat64 = math.SmallestNonzeroFloat64
    54  )
    55  
    56  const (
    57  	_ = assert(smallestFloat32 > 0)
    58  	_ = assert(smallestFloat64 > 0)
    59  )
    60  
    61  const (
    62  	maxFloat32 = 1<<127 * (1<<24 - 1) / (1.0<<23)
    63  	// TODO(gri) The compiler limits integers to 512 bit and thus
    64  	//           we cannot compute the value 1<<1023
    65  	//           without overflow. For now we match the compiler.
    66  	//           See also issue #44057.
    67  	// maxFloat64 = 1<<1023 * (1<<53 - 1) / (1.0<<52)
    68  	maxFloat64 = math.MaxFloat64
    69  )
    70  
    71  const (
    72  	_ int8 = minInt8 /* ERROR "overflows" */ - 1
    73  	_ int8 = minInt8
    74  	_ int8 = maxInt8
    75  	_ int8 = maxInt8 /* ERROR "overflows" */ + 1
    76  	_ int8 = smallestFloat64 /* ERROR "truncated" */
    77  
    78  	_ = int8(minInt8 /* ERROR "overflows" */ - 1)
    79  	_ = int8(minInt8)
    80  	_ = int8(maxInt8)
    81  	_ = int8(maxInt8 /* ERROR "overflows" */ + 1)
    82  	_ = int8(smallestFloat64 /* ERROR "cannot convert" */)
    83  )
    84  
    85  const (
    86  	_ int16 = minInt16 /* ERROR "overflows" */ - 1
    87  	_ int16 = minInt16
    88  	_ int16 = maxInt16
    89  	_ int16 = maxInt16 /* ERROR "overflows" */ + 1
    90  	_ int16 = smallestFloat64 /* ERROR "truncated" */
    91  
    92  	_ = int16(minInt16 /* ERROR "overflows" */ - 1)
    93  	_ = int16(minInt16)
    94  	_ = int16(maxInt16)
    95  	_ = int16(maxInt16 /* ERROR "overflows" */ + 1)
    96  	_ = int16(smallestFloat64 /* ERROR "cannot convert" */)
    97  )
    98  
    99  const (
   100  	_ int32 = minInt32 /* ERROR "overflows" */ - 1
   101  	_ int32 = minInt32
   102  	_ int32 = maxInt32
   103  	_ int32 = maxInt32 /* ERROR "overflows" */ + 1
   104  	_ int32 = smallestFloat64 /* ERROR "truncated" */
   105  
   106  	_ = int32(minInt32 /* ERROR "overflows" */ - 1)
   107  	_ = int32(minInt32)
   108  	_ = int32(maxInt32)
   109  	_ = int32(maxInt32 /* ERROR "overflows" */ + 1)
   110  	_ = int32(smallestFloat64 /* ERROR "cannot convert" */)
   111  )
   112  
   113  const (
   114  	_ int64 = minInt64 /* ERROR "overflows" */ - 1
   115  	_ int64 = minInt64
   116  	_ int64 = maxInt64
   117  	_ int64 = maxInt64 /* ERROR "overflows" */ + 1
   118  	_ int64 = smallestFloat64 /* ERROR "truncated" */
   119  
   120  	_ = int64(minInt64 /* ERROR "overflows" */ - 1)
   121  	_ = int64(minInt64)
   122  	_ = int64(maxInt64)
   123  	_ = int64(maxInt64 /* ERROR "overflows" */ + 1)
   124  	_ = int64(smallestFloat64 /* ERROR "cannot convert" */)
   125  )
   126  
   127  const (
   128  	_ int = minInt /* ERROR "overflows" */ - 1
   129  	_ int = minInt
   130  	_ int = maxInt
   131  	_ int = maxInt /* ERROR "overflows" */ + 1
   132  	_ int = smallestFloat64 /* ERROR "truncated" */
   133  
   134  	_ = int(minInt /* ERROR "overflows" */ - 1)
   135  	_ = int(minInt)
   136  	_ = int(maxInt)
   137  	_ = int(maxInt /* ERROR "overflows" */ + 1)
   138  	_ = int(smallestFloat64 /* ERROR "cannot convert" */)
   139  )
   140  
   141  const (
   142  	_ uint8 = 0 /* ERROR "overflows" */ - 1
   143  	_ uint8 = 0
   144  	_ uint8 = maxUint8
   145  	_ uint8 = maxUint8 /* ERROR "overflows" */ + 1
   146  	_ uint8 = smallestFloat64 /* ERROR "truncated" */
   147  
   148  	_ = uint8(0 /* ERROR "overflows" */ - 1)
   149  	_ = uint8(0)
   150  	_ = uint8(maxUint8)
   151  	_ = uint8(maxUint8 /* ERROR "overflows" */ + 1)
   152  	_ = uint8(smallestFloat64 /* ERROR "cannot convert" */)
   153  )
   154  
   155  const (
   156  	_ uint16 = 0 /* ERROR "overflows" */ - 1
   157  	_ uint16 = 0
   158  	_ uint16 = maxUint16
   159  	_ uint16 = maxUint16 /* ERROR "overflows" */ + 1
   160  	_ uint16 = smallestFloat64 /* ERROR "truncated" */
   161  
   162  	_ = uint16(0 /* ERROR "overflows" */ - 1)
   163  	_ = uint16(0)
   164  	_ = uint16(maxUint16)
   165  	_ = uint16(maxUint16 /* ERROR "overflows" */ + 1)
   166  	_ = uint16(smallestFloat64 /* ERROR "cannot convert" */)
   167  )
   168  
   169  const (
   170  	_ uint32 = 0 /* ERROR "overflows" */ - 1
   171  	_ uint32 = 0
   172  	_ uint32 = maxUint32
   173  	_ uint32 = maxUint32 /* ERROR "overflows" */ + 1
   174  	_ uint32 = smallestFloat64 /* ERROR "truncated" */
   175  
   176  	_ = uint32(0 /* ERROR "overflows" */ - 1)
   177  	_ = uint32(0)
   178  	_ = uint32(maxUint32)
   179  	_ = uint32(maxUint32 /* ERROR "overflows" */ + 1)
   180  	_ = uint32(smallestFloat64 /* ERROR "cannot convert" */)
   181  )
   182  
   183  const (
   184  	_ uint64 = 0 /* ERROR "overflows" */ - 1
   185  	_ uint64 = 0
   186  	_ uint64 = maxUint64
   187  	_ uint64 = maxUint64 /* ERROR "overflows" */ + 1
   188  	_ uint64 = smallestFloat64 /* ERROR "truncated" */
   189  
   190  	_ = uint64(0 /* ERROR "overflows" */ - 1)
   191  	_ = uint64(0)
   192  	_ = uint64(maxUint64)
   193  	_ = uint64(maxUint64 /* ERROR "overflows" */ + 1)
   194  	_ = uint64(smallestFloat64 /* ERROR "cannot convert" */)
   195  )
   196  
   197  const (
   198  	_ uint = 0 /* ERROR "overflows" */ - 1
   199  	_ uint = 0
   200  	_ uint = maxUint
   201  	_ uint = maxUint /* ERROR "overflows" */ + 1
   202  	_ uint = smallestFloat64 /* ERROR "truncated" */
   203  
   204  	_ = uint(0 /* ERROR "overflows" */ - 1)
   205  	_ = uint(0)
   206  	_ = uint(maxUint)
   207  	_ = uint(maxUint /* ERROR "overflows" */ + 1)
   208  	_ = uint(smallestFloat64 /* ERROR "cannot convert" */)
   209  )
   210  
   211  const (
   212  	_ uintptr = 0 /* ERROR "overflows" */ - 1
   213  	_ uintptr = 0
   214  	_ uintptr = maxUintptr
   215  	_ uintptr = maxUintptr /* ERROR "overflows" */ + 1
   216  	_ uintptr = smallestFloat64 /* ERROR "truncated" */
   217  
   218  	_ = uintptr(0 /* ERROR "overflows" */ - 1)
   219  	_ = uintptr(0)
   220  	_ = uintptr(maxUintptr)
   221  	_ = uintptr(maxUintptr /* ERROR "overflows" */ + 1)
   222  	_ = uintptr(smallestFloat64 /* ERROR "cannot convert" */)
   223  )
   224  
   225  const (
   226  	_ float32 = minInt64
   227  	_ float64 = minInt64
   228  	_ complex64 = minInt64
   229  	_ complex128 = minInt64
   230  
   231  	_ = float32(minInt64)
   232  	_ = float64(minInt64)
   233  	_ = complex64(minInt64)
   234  	_ = complex128(minInt64)
   235  )
   236  
   237  const (
   238  	_ float32 = maxUint64
   239  	_ float64 = maxUint64
   240  	_ complex64 = maxUint64
   241  	_ complex128 = maxUint64
   242  
   243  	_ = float32(maxUint64)
   244  	_ = float64(maxUint64)
   245  	_ = complex64(maxUint64)
   246  	_ = complex128(maxUint64)
   247  )
   248  
   249  // TODO(gri) find smaller deltas below
   250  
   251  const delta32 = maxFloat32/(1 << 23)
   252  
   253  const (
   254  	_ float32 = - /* ERROR "overflow" */ (maxFloat32 + delta32)
   255  	_ float32 = -maxFloat32
   256  	_ float32 = maxFloat32
   257  	_ float32 = maxFloat32 /* ERROR "overflow" */ + delta32
   258  
   259  	_ = float32(- /* ERROR "cannot convert" */ (maxFloat32 + delta32))
   260  	_ = float32(-maxFloat32)
   261  	_ = float32(maxFloat32)
   262  	_ = float32(maxFloat32 /* ERROR "cannot convert" */ + delta32)
   263  
   264  	_ = assert(float32(smallestFloat32) == smallestFloat32)
   265  	_ = assert(float32(smallestFloat32/2) == 0)
   266  	_ = assert(float32(smallestFloat64) == 0)
   267  	_ = assert(float32(smallestFloat64/2) == 0)
   268  )
   269  
   270  const delta64 = maxFloat64/(1 << 52)
   271  
   272  const (
   273  	_ float64 = - /* ERROR "overflow" */ (maxFloat64 + delta64)
   274  	_ float64 = -maxFloat64
   275  	_ float64 = maxFloat64
   276  	_ float64 = maxFloat64 /* ERROR "overflow" */ + delta64
   277  
   278  	_ = float64(- /* ERROR "cannot convert" */ (maxFloat64 + delta64))
   279  	_ = float64(-maxFloat64)
   280  	_ = float64(maxFloat64)
   281  	_ = float64(maxFloat64 /* ERROR "cannot convert" */ + delta64)
   282  
   283  	_ = assert(float64(smallestFloat32) == smallestFloat32)
   284  	_ = assert(float64(smallestFloat32/2) == smallestFloat32/2)
   285  	_ = assert(float64(smallestFloat64) == smallestFloat64)
   286  	_ = assert(float64(smallestFloat64/2) == 0)
   287  )
   288  
   289  const (
   290  	_ complex64 = - /* ERROR "overflow" */ (maxFloat32 + delta32)
   291  	_ complex64 = -maxFloat32
   292  	_ complex64 = maxFloat32
   293  	_ complex64 = maxFloat32 /* ERROR "overflow" */ + delta32
   294  
   295  	_ = complex64(- /* ERROR "cannot convert" */ (maxFloat32 + delta32))
   296  	_ = complex64(-maxFloat32)
   297  	_ = complex64(maxFloat32)
   298  	_ = complex64(maxFloat32 /* ERROR "cannot convert" */ + delta32)
   299  )
   300  
   301  const (
   302  	_ complex128 = - /* ERROR "overflow" */ (maxFloat64 + delta64)
   303  	_ complex128 = -maxFloat64
   304  	_ complex128 = maxFloat64
   305  	_ complex128 = maxFloat64 /* ERROR "overflow" */ + delta64
   306  
   307  	_ = complex128(- /* ERROR "cannot convert" */ (maxFloat64 + delta64))
   308  	_ = complex128(-maxFloat64)
   309  	_ = complex128(maxFloat64)
   310  	_ = complex128(maxFloat64 /* ERROR "cannot convert" */ + delta64)
   311  )
   312  
   313  // Initialization of typed constant and conversion are the same:
   314  const (
   315  	f32 = 1 + smallestFloat32
   316  	x32 float32 = f32
   317  	y32 = float32(f32)
   318  	_ = assert(x32 - y32 == 0)
   319  )
   320  
   321  const (
   322  	f64 = 1 + smallestFloat64
   323  	x64 float64 = f64
   324  	y64 = float64(f64)
   325  	_ = assert(x64 - y64 == 0)
   326  )
   327  
   328  const (
   329  	_ = int8(-1) << 7
   330  	_ = int8 /* ERROR "overflows" */ (-1) << 8
   331  
   332  	_ = uint32(1) << 31
   333  	_ = uint32 /* ERROR "overflows" */ (1) << 32
   334  )
   335
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