typetraits: add toSigned, toUnsigned

Author: timotheecour

lib/pure/typetraits.nim

@@ -30,6 +30,14 @@ runnableExamples:
   type C[T] = enum h0 = 2, h1 = 4
   assert C[float] is HoleyEnum
 
+runnableExamples:
+  # `toSigned`, `toUnsigned`
+  assert int8.toSigned is int8
+  assert int8.toUnsigned is uint8
+  assert uint.toUnsigned is uint
+  assert int.toUnsigned is uint
+  assert $int32.toUnsigned == "uint32"
+
 proc name*(t: typedesc): string {.magic: "TypeTrait".} =
   ## Returns the name of the given type.
   ##
@@ -284,3 +292,7 @@ proc hasClosure*(fn: NimNode): bool {.since: (1, 5, 1).} =
   ## arguments and not `untyped` arguments.
   expectKind fn, nnkSym
   result = hasClosureImpl(fn)
+
+from std/private/vmutils import toUnsigned, toSigned
+
+export toUnsigned, toSigned

lib/std/private/vmutils.nim

@@ -1,3 +1,5 @@
+# xxx rename to something more meaningful
+
 template forwardImpl*(impl, arg) {.dirty.} =
   when sizeof(x) <= 4:
     when x is SomeSignedInt:

lib/system/strmantle.nim

@@ -10,7 +10,7 @@
 # Compilerprocs for strings that do not depend on the string implementation.
 
 import std/private/digitsutils
-import std/private/vmutils
+
 
 proc cmpStrings(a, b: string): int {.inline, compilerproc.} =
   let alen = a.len
@@ -43,17 +43,6 @@ proc hashString(s: string): int {.compilerproc.} =
   h = h + h shl 15
   result = cast[int](h)
 
-proc absUnsigned[T](x: T): auto {.inline.} =
-  ## computes `abs(x)` as unsigned without branching, taking care of `T.low`
-  type T2 = toUnsigned(T)
-  result = (not cast[T2](x)) + 1
-  when false:
-    # faster than branching via:
-    if x == low(T):
-      num = T2(x)
-    else:
-      num = T2(-x)
-
 proc addInt*(result: var string; x: int64) =
   ## Converts integer to its string representation and appends it to `result`.
   ##
@@ -63,9 +52,12 @@ proc addInt*(result: var string; x: int64) =
   ##     b = 45
   ##   a.addInt(b) # a <- "12345"
   var num: uint64
+
   if x < 0:
-    # num = absUnsigned(x)
-    num =  (not cast[uint64](x)) + 1
+    if x == low(int64):
+      num = uint64(x)
+    else:
+      num = uint64(-x)
     let base = result.len
     setLen(result, base + 1)
     result[base] = '-'

tests/metatype/ttypetraits.nim

@@ -1,6 +1,18 @@
 import typetraits
 import macros
 
+block: # toUnsigned, toSigned
+  var a1: toSigned(int16)
+  doAssert a1 is int16
+  var a2: toSigned(uint16)
+  doAssert $a2.typeof == "int16"
+  doAssert toSigned(uint32) is int32
+  doAssert uint64.toSigned is int64
+  doAssert int64.toSigned is int64
+  doAssert int64.toUnsigned is uint64
+  doAssert int.toUnsigned is uint
+  doAssert $uint.toUnsigned == "uint"
+
 block: # isNamedTuple
   type Foo1 = (a:1,).type
   type Foo2 = (Field0:1,).type

tests/stdlib/ttypetraits.nim

@@ -2,9 +2,9 @@ discard """
   targets: "c cpp js"
 """
 
-import std/typetraits
-
+# xxx merge with tests/metatype/ttypetraits.nim
 
+import std/typetraits
 
 macro testClosure(fn: typed, flag: static bool) =
   if flag: