signed int initialization

stint/intops.nim

@@ -32,11 +32,11 @@ func sign*(a: StInt): int =
 func isNegative*(a: StInt): bool =
   a.sign < 0
 
-func clearSign(a: var StInt) =
-  a.limbs[^1] = a.limbs[^1] and clearSignMask
+func clearMSB(a: var StInt) =
+  a.limbs[0] = a.limbs[0] and clearSignMask
 
-func setSign(a: var StInt) =
-  a.limbs[^1] = a.limbs[^1] or signMask
+func setMSB(a: var StInt) =
+  a.limbs[0] = a.limbs[0] or signMask
 
 func negate*(a: var StInt) =
   a.imp.bitnot(a.imp)
@@ -82,14 +82,14 @@ func high*[bits](_: typedesc[StInt[bits]]): StInt[bits] =
   # so we only have to unset the most significant bit.
   for i in 0 ..< result.limbs.len:
     result[i] = high(Word)
-  result.clearSign
+  result.clearMSB
 
 func low*[bits](_: typedesc[StInt[bits]]): StInt[bits] =
   # The lowest signed int has representation
   # 0b1000_0000_0000_0000 ....
   # so we only have to set the most significant bit.
   result.setZero
-  result.setSign
+  result.setMSB
 
 {.pop.}
 

stint/private/datatypes.nim

@@ -97,11 +97,17 @@ func usedBitsAndWords*(a: openArray[Word]): tuple[bits, words: int] =
 template limbs*(a: StInt): untyped =
   # TODO: remove this when we switch to borrow `.`
   a.imp.limbs
+
+template `[]`*(a: StInt, i: SomeInteger or BackwardsIndex): Word =
+  a.imp.limbs[i]
+
+template `[]=`*(a: var StInt, i: SomeInteger or BackwardsIndex, val: Word) =
+  a.imp.limbs[i] = val
   
-template `[]`*(a: SomeBigInteger, i: SomeInteger or BackwardsIndex): Word =
+template `[]`*(a: StUInt, i: SomeInteger or BackwardsIndex): Word =
   a.limbs[i]
 
-template `[]=`*(a: var SomeBigInteger, i: SomeInteger or BackwardsIndex, val: Word) =
+template `[]=`*(a: var StUInt, i: SomeInteger or BackwardsIndex, val: Word) =
   a.limbs[i] = val
 
 # Iterations

stint/uintops.nim

@@ -15,7 +15,8 @@ import
   ./private/uint_addsub,
   ./private/uint_mul,
   ./private/uint_div,
-  ./private/primitives/addcarry_subborrow
+  ./private/primitives/addcarry_subborrow,
+  stew/bitops2
 
 export StUint
 
@@ -133,6 +134,16 @@ func `shl`*(a: StUint, k: SomeInteger): StUint =
   ## Shift left by k bits
   result.shiftLeft(a, k)
 
+func setBit*(a: var StUint, k: SomeInteger) =
+  let limbIndex = k div WordBitWidth
+  let bitIndex = k mod WordBitWidth
+  setBit(a.limbs[limbIndex], bitIndex)
+
+func clearBit*(a: var StUint, k: SomeInteger) =
+  let limbIndex = k div WordBitWidth
+  let bitIndex = k mod WordBitWidth
+  clearBit(a.limbs[limbIndex], bitIndex)
+
 {.pop.}
 
 # Addsub

tests/test_int_initialization.nim

@@ -0,0 +1,57 @@
+# Stint
+# Copyright 2018-2023 Status Research & Development GmbH
+# Licensed under either of
+#
+#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+#
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+import ../stint, unittest, test_helpers
+
+template testInitialization(chk, tst: untyped) =
+  tst "zero one":
+    var a: StInt[128]
+    a.setZero
+    chk a == 0.i128
+
+    var b: StInt[256]
+    b.setZero
+    chk b == 0.i256
+
+    var aa: StInt[128]
+    aa.setOne
+    chk aa == 1.i128
+
+    var bb: StInt[256]
+    bb.setOne
+    chk bb == 1.i256
+
+    var xx = StInt[128].zero
+    chk xx == 0.i128
+
+    var yy = StInt[256].zero
+    chk yy == 0.i256
+
+    var uu = StInt[128].one
+    chk uu == 1.i128
+
+    var vv = StInt[256].one
+    chk vv == 1.i256
+
+  tst "hi lo":
+    let x = Int128.high
+    var z = UInt128.high
+    z.clearBit(0)
+    chk x.imp == z
+
+    let xx = Int128.low
+    var zz = UInt128.low
+    zz.setBit(0)
+    chk xx.imp == zz
+
+static:
+  testInitialization(ctCheck, ctTest)
+
+suite "Signed integer initialization":
+  testInitialization(check, test)

tests/test_int_signedness.nim

@@ -9,14 +9,6 @@
 
 import ../stint, unittest, test_helpers
 
-#[
-template chkAddition(chk, a, b, c, bits: untyped) =
-  block:
-    let x = stuint(a, bits)
-    let y = stuint(b, bits)
-    chk x + y == stuint(c, bits)
-]#
-
 template testSignedness(chk, tst: untyped) =
   tst "positive sign":
     let a = stint(1, 128)