The maximum value for an int type in Go

Question

How does one specify the maximum value representable for an unsigned integer type   I would like to know how to initialize min in the loop below that iteratively computes min and max lengths from some structs   var minLen uint       var maxLen uint   0 for    thing    range sliceOfThings     if minLen  gt  thing n   minLen   thing n     if maxLen  lt  thing n   maxLen   thing n     if minLen  gt  maxLen        If there are no values  clamp min at 0 so that min  lt   max    minLen   0     so that the first time through the comparison  minLen  gt   n

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https   groups google com group golang-nuts msg 71c307e4d73024ce pli 1  The germane part      Since integer types use two s complement arithmetic  you can infer the    min max constant values for int and uint  For example   const MaxUint    uint 0   const MinUint   0  const MaxInt   int MaxUint  gt  gt  1   const MinInt   -MaxInt - 1    As per  CarelZA s comment   uint8    0 to 255  uint16   0 to 65535  uint32   0 to 4294967295  uint64   0 to 18446744073709551615  int8     -128 to 127  int16    -32768 to 32767  int32    -2147483648 to 2147483647  int64    -9223372036854775808 to 9223372036854775807

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Quick summary   import  math bits  const       MaxUint uint    1  lt  lt  bits UintSize  - 1     MaxInt int    1  lt  lt  bits UintSize    2 - 1     MinInt int    1  lt  lt  bits UintSize    -2     Background   As I presume you know  the uint type is the same size as either uint32 or uint64  depending on the platform you re on  Usually  one would use the unsized version of these only when there is no risk of coming close to the maximum value  as the version without a size specification can use the  native  type  depending on platform  which tends to be faster   Note that it tends to be  faster  because using a non-native type sometimes requires additional math and bounds-checking to be performed by the processor  in order to emulate the larger or smaller integer  With that in mind  be aware that the performance of the processor  or compiler s optimised code  is almost always going to be better than adding your own bounds-checking code  so if there is any risk of it coming into play  it may make sense to simply use the fixed-size version  and let the optimised emulation handle any fallout from that   With that having been said  there are still some situations where it is useful to know what you re working with   The package  math bits  contains the size of uint  in bits  To determine the maximum value  shift 1 by that many bits  minus 1  ie   1  lt  lt  bits UintSize  - 1  Note that when calculating the maximum value of uint  you ll generally need to put it explicitly into a uint  or larger  variable  otherwise the compiler may fail  as it will default to attempting to assign that calculation into a signed int  where  as should be obvious  it would not fit   so   const MaxUint uint    1  lt  lt  bits UintSize  - 1   That s the direct answer to your question  but there are also a couple of related calculations you may be interested in   According to the spec  uint and int are always the same size      uint     either 32 or 64 bits      int      same size as uint   So we can also use this constant to determine the maximum value of int  by taking that same answer and dividing by 2 then subtracting 1  ie   1  lt  lt  bits UintSize    2 - 1  And the minimum value of int  by shifting 1 by that many bits and dividing the result by -2  ie   1  lt  lt  bits UintSize    -2  In summary   MaxUint   1  lt  lt  bits UintSize  - 1  MaxInt   1  lt  lt  bits UintSize    2 - 1  MinInt   1  lt  lt  bits UintSize    -2  full example  should be the same as below   package main  import  fmt  import  math  import  math bits   func main         var mi32 int64   math MinInt32     var mi64 int64   math MinInt64      var i32 uint64   math MaxInt32     var ui32 uint64   math MaxUint32     var i64 uint64   math MaxInt64     var ui64 uint64   math MaxUint64     var ui uint64    1  lt  lt  bits UintSize  - 1     var i uint64    1  lt  lt  bits UintSize    2 - 1     var mi int64    1  lt  lt  bits UintSize    -2      fmt Printf   MinInt32   d n   mi32      fmt Printf   MaxInt32    d n   i32      fmt Printf  MaxUint32    d n   ui32      fmt Printf   MinInt64   d n   mi64      fmt Printf   MaxInt64    d n   i64      fmt Printf  MaxUint64    d n   ui64      fmt Printf    MaxUint    d n   ui      fmt Printf     MinInt   d n   mi      fmt Printf     MaxInt    d n   i

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MaxInt8     1 lt  lt 7 - 1 MinInt8     -1  lt  lt  7 MaxInt16    1 lt  lt 15 - 1 MinInt16    -1  lt  lt  15 MaxInt32    1 lt  lt 31 - 1 MinInt32    -1  lt  lt  31 MaxInt64    1 lt  lt 63 - 1 MinInt64    -1  lt  lt  63 MaxUint8    1 lt  lt 8 - 1 MaxUint16   1 lt  lt 16 - 1 MaxUint32   1 lt  lt 32 - 1 MaxUint64   1 lt  lt 64 - 1

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From math lib  https   github com golang go blob master src math const go L39  package main  import        fmt       math     func main         fmt Printf  max int64   d n   math MaxInt64

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A lightweight package contains them  as well as other int types limits and some widely used integer functions    import        fmt        lt Full URL gt  go-imath ix        lt Full URL gt  go-imath ux        fmt Println ix Minimal     Output  -2147483648  32-bit  or -9223372036854775808  64-bit  fmt Println ix Maximal     Output  2147483647 or 9223372036854775807 fmt Println ux Minimal     Output  0 fmt Println ux Maximal     Output  4294967295 or 18446744073709551615

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Use the constants defined in the math package  const       MaxInt8     1 lt  lt 7 - 1     MinInt8     -1  lt  lt  7     MaxInt16    1 lt  lt 15 - 1     MinInt16    -1  lt  lt  15     MaxInt32    1 lt  lt 31 - 1     MinInt32    -1  lt  lt  31     MaxInt64    1 lt  lt 63 - 1     MinInt64    -1  lt  lt  63     MaxUint8    1 lt  lt 8 - 1     MaxUint16   1 lt  lt 16 - 1     MaxUint32   1 lt  lt 32 - 1     MaxUint64   1 lt  lt 64 - 1

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I would use math package for getting the maximal value and minimal value     func printMinMaxValue            integer max     fmt Printf  max int64     v n   math MaxInt64      fmt Printf  max int32     v n   math MaxInt32      fmt Printf  max int16     v n   math MaxInt16          integer min     fmt Printf  min int64     v n   math MinInt64      fmt Printf  min int32     v n   math MinInt32       fmt Printf  max flloat64    v n   math MaxFloat64      fmt Printf  max float32    v n   math MaxFloat32          etc you can see more int the  math package     Ouput    max int64   9223372036854775807 max int32   2147483647 max int16   32767 min int64   -9223372036854775808 min int32   -2147483648 max flloat64  1 7976931348623157e 308 max float32  3 4028234663852886e 38

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https   golang org ref spec Numeric types for physical type limits   The max values are defined in the math package so in your case  math MaxUint32  Watch out as there is no overflow - incrementing past max causes wraparound

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I originally used the code taken from the discussion thread that  nmichaels used in his answer  I now use a slightly different calculation  I ve included some comments in case anyone else has the same query as  Arijoon  const       MinUint uint   0                    binary  all zeroes         Perform a bitwise NOT to change every bit from 0 to 1     MaxUint         MinUint             binary  all ones         Shift the binary number to the right  i e  divide by two         to change the high bit to 0     MaxInt         int MaxUint  gt  gt  1     binary  all ones except high bit         Perform another bitwise NOT to change the high bit to 1 and        all other bits to 0     MinInt          MaxInt              binary  all zeroes except high bit     The last two steps work because of how positive and negative numbers are represented in two s complement arithmetic  The Go language specification section on Numeric types refers the reader to the relevant Wikipedia article  I haven t read that  but I did learn about two s complement from the book Code by Charles Petzold  which is a very accessible intro to the fundamentals of computers and coding   I put the code above  minus most of the comments  in to a little integer math package

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One way to solve this problem is to get the starting points from the values themselves   var minLen  maxLen uint if len sliceOfThings   gt  0     minLen   sliceOfThings 0  minLen   maxLen   sliceOfThings 0  maxLen   for    thing    range sliceOfThings 1         if minLen  gt  thing minLen   minLen   thing minLen       if maxLen  lt  thing maxLen   maxLen   thing maxLen

[numbers] The maximum value for an int type in Go

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