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std/hashes: hash(ref|ptr|pointer) + other improvements (nim-lang#17731)
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timotheecour authored and PMunch committed Mar 28, 2022
1 parent e84ec60 commit c44d564
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Showing 5 changed files with 89 additions and 29 deletions.
72 changes: 49 additions & 23 deletions lib/pure/hashes.nim
Original file line number Diff line number Diff line change
Expand Up @@ -182,7 +182,7 @@ proc hashData*(data: pointer, size: int): Hash =
var h: Hash = 0
when defined(js):
var p: cstring
asm """`p` = `Data`;"""
asm """`p` = `Data`"""
else:
var p = cast[cstring](data)
var i = 0
Expand All @@ -193,12 +193,22 @@ proc hashData*(data: pointer, size: int): Hash =
dec(s)
result = !$h

proc hashIdentity*[T: Ordinal|enum](x: T): Hash {.inline, since: (1, 3).} =
## The identity hash, i.e. `hashIdentity(x) = x`.
cast[Hash](ord(x))

when defined(nimIntHash1):
proc hash*[T: Ordinal|enum](x: T): Hash {.inline.} =
## Efficient hashing of integers.
cast[Hash](ord(x))
else:
proc hash*[T: Ordinal|enum](x: T): Hash {.inline.} =
## Efficient hashing of integers.
hashWangYi1(uint64(ord(x)))

when defined(js):
var objectID = 0

proc hash*(x: pointer): Hash {.inline.} =
## Efficient hashing of pointers.
when defined(js):
proc getObjectId(x: pointer): int =
asm """
if (typeof `x` == "object") {
if ("_NimID" in `x`)
Expand All @@ -209,29 +219,46 @@ proc hash*(x: pointer): Hash {.inline.} =
}
}
"""

proc hash*(x: pointer): Hash {.inline.} =
## Efficient `hash` overload.
when defined(js):
let y = getObjectId(x)
else:
result = cast[Hash](cast[uint](x) shr 3) # skip the alignment
let y = cast[int](x)
hash(y) # consistent with code expecting scrambled hashes depending on `nimIntHash1`.

proc hash*[T](x: ref[T] | ptr[T]): Hash {.inline.} =
## Efficient `hash` overload.
runnableExamples:
var a: array[10, uint8]
assert a[0].addr.hash != a[1].addr.hash
assert cast[pointer](a[0].addr).hash == a[0].addr.hash
runnableExamples:
type A = ref object
x: int
let a = A(x: 3)
let ha = a.hash
assert ha != A(x: 3).hash # A(x: 3) is a different ref object from `a`.
a.x = 4
assert ha == a.hash # the hash only depends on the address
runnableExamples:
# you can overload `hash` if you want to customize semantics
type A[T] = ref object
x, y: T
proc hash(a: A): Hash = hash(a.x)
assert A[int](x: 3, y: 4).hash == A[int](x: 3, y: 5).hash
# xxx pending bug #17733, merge as `proc hash*(pointer | ref | ptr): Hash`
# or `proc hash*[T: ref | ptr](x: T): Hash`
hash(cast[pointer](x))

proc hash*[T: proc](x: T): Hash {.inline.} =
## Efficient hashing of proc vars. Closures are supported too.
when T is "closure":
result = hash(rawProc(x)) !& hash(rawEnv(x))
result = hash((rawProc(x), rawEnv(x)))
else:
result = hash(pointer(x))

proc hashIdentity*[T: Ordinal|enum](x: T): Hash {.inline, since: (1, 3).} =
## The identity hash, i.e. `hashIdentity(x) = x`.
cast[Hash](ord(x))

when defined(nimIntHash1):
proc hash*[T: Ordinal|enum](x: T): Hash {.inline.} =
## Efficient hashing of integers.
cast[Hash](ord(x))
else:
proc hash*[T: Ordinal|enum](x: T): Hash {.inline.} =
## Efficient hashing of integers.
hashWangYi1(uint64(ord(x)))

proc hash*(x: float): Hash {.inline.} =
## Efficient hashing of floats.
let y = x + 0.0 # for denormalization
Expand Down Expand Up @@ -484,10 +511,9 @@ proc hashIgnoreCase*(sBuf: string, sPos, ePos: int): Hash =
h = h !& ord(c)
result = !$h


proc hash*[T: tuple | object](x: T): Hash =
## Efficient hashing of tuples and objects.
## There must be a `hash` proc defined for each of the field types.
## Efficient `hash` overload.
## `hash` must be defined for each component of `x`.
runnableExamples:
type Obj = object
x: int
Expand Down
4 changes: 4 additions & 0 deletions testament/lib/stdtest/testutils.nim
Original file line number Diff line number Diff line change
Expand Up @@ -85,3 +85,7 @@ template accept*(a) =

template reject*(a) =
doAssert not compiles(a)

template disableVm*(body) =
when nimvm: discard
else: body
14 changes: 14 additions & 0 deletions tests/collections/ttables.nim
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,11 @@ And we get here
3
'''
joinable: false
targets: "c cpp js"
"""

# xxx wrap in a template to test in VM, see https://github.com/timotheecour/Nim/issues/534#issuecomment-769565033

import hashes, sequtils, tables, algorithm

proc sortedPairs[T](t: T): auto = toSeq(t.pairs).sorted
Expand Down Expand Up @@ -444,3 +448,13 @@ block emptyOrdered:
var t2: OrderedTable[int, string]
doAssert t1 == t2

block: # Table[ref, int]
type A = ref object
x: int
var t: OrderedTable[A, int]
let a1 = A(x: 3)
let a2 = A(x: 3)
t[a1] = 10
t[a2] = 11
doAssert t[a1] == 10
doAssert t[a2] == 11
22 changes: 21 additions & 1 deletion tests/stdlib/thashes.nim
Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ discard """
"""

import std/hashes

from stdtest/testutils import disableVm, whenVMorJs

when not defined(js) and not defined(cpp):
block:
Expand Down Expand Up @@ -177,5 +177,25 @@ proc main() =
doAssert hash(Obj5(t: false, x: 1)) == hash(Obj5(t: true, y: 1))
doAssert hash(Obj5(t: false, x: 1)) != hash(Obj5(t: true, y: 2))

block: # hash(ref|ptr|pointer)
var a: array[10, uint8]
# disableVm:
whenVMorJs:
# pending fix proposed in https://github.com/nim-lang/Nim/issues/15952#issuecomment-786312417
discard
do:
assert a[0].addr.hash != a[1].addr.hash
assert cast[pointer](a[0].addr).hash == a[0].addr.hash

block: # hash(ref)
type A = ref object
x: int
let a = A(x: 3)
disableVm: # xxx Error: VM does not support 'cast' from tyRef to tyPointer
let ha = a.hash
assert ha != A(x: 3).hash # A(x: 3) is a different ref object from `a`.
a.x = 4
assert ha == a.hash # the hash only depends on the address

static: main()
main()
6 changes: 1 addition & 5 deletions tests/stdlib/tstrutils.nim
Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ discard """
"""

import std/strutils

from stdtest/testutils import disableVm
# xxx each instance of `disableVm` and `when not defined js:` should eventually be fixed

template rejectParse(e) =
Expand All @@ -12,10 +12,6 @@ template rejectParse(e) =
raise newException(AssertionDefect, "This was supposed to fail: $#!" % astToStr(e))
except ValueError: discard

template disableVm(body) =
when nimvm: discard
else: body

template main() =
block: # strip
doAssert strip(" ha ") == "ha"
Expand Down

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