tidying up compiletime helpers

stint/endians2.nim

@@ -7,7 +7,7 @@
 #
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
-import private/[bitops2_priv, endians2_priv, datatypes]
+import private/[bitops2_priv, endians2_priv, datatypes, compiletime_helpers]
 
 import stew/endians2
 export endians2
@@ -30,7 +30,10 @@ func fromBytes*[bits: static int](
     T: typedesc[StUint[bits]],
     x: array[bits div 8, byte],
     endian: Endianness = system.cpuEndian): T {.inline, noinit.} =
-  # TODO compile-time version
+
+  when nimvm:
+    copyFromArray(result.data, x)
+  else:
     copyMem(addr result, unsafeAddr x[0], bits div 8)
 
   if endian != system.cpuEndian:

stint/private/compiletime_helpers.nim

@@ -1,4 +1,4 @@
-import ./datatypes, ./uint_bitwise_ops
+import ./datatypes, ./uint_bitwise_ops, ./bitops2_priv
 
 func convertImpl[T: SomeInteger](x: SomeInteger): T {.compileTime.} =
   cast[T](x)
@@ -22,3 +22,38 @@ func getByte*(x: SomeInteger, pos: int): byte {.compileTime.} =
 func getByte*(x: UintImpl | IntImpl, pos: int): byte {.compileTime.} =
   type DT = type x.leastSignificantWord
   byte((x shr (pos * 8)).leastSignificantWord and 0xFF.DT)
+
+proc setByte*(x: var SomeInteger, pos: int, b: byte) {.compileTime.} =
+  type DT = type x
+  x = x or (DT(b) shl (pos*8))
+
+type SomeIntImpl = UintImpl | IntImpl
+func setByte*(x: var SomeIntImpl, pos: int, b: byte) {.compileTime.} =
+  proc putFirstByte(x: var SomeInteger, b: byte) =
+    type DT = type x
+    x = x or b.DT
+
+  proc putFirstByte(x: var UintImpl, b: byte) =
+    putFirstByte(x.lo, b)
+
+  var cx: type x
+  cx.putFirstByte(b)
+  x = x or (cx shl (pos*8))
+
+func copyToArray*(ret: var openArray[byte], x: UintImpl) {.compileTime.} =
+  const size = bitsof(x) div 8
+  doAssert ret.len >= size
+  for i in 0 ..< size:
+    ret[i] = x.getByte(i)
+
+func copyFromArray*(x: var UintImpl, data: openArray[byte]) {.compileTime.} =
+  const size = bitsof(x) div 8
+  doAssert data.len >= size
+  for i in 0 ..< size:
+    x.setByte(i, data[i])
+
+func copyFromArray*(x: var SomeInteger, data: openArray[byte]) {.compileTime.} =
+  const size = bitsof(x) div 8
+  doAssert data.len >= size
+  for i in 0 ..< size:
+    x.setByte(i, data[i])

stint/private/endians2_priv.nim

@@ -8,21 +8,15 @@ func swapBytes*(x: UintImpl): UintImpl {.inline.} =
 
   UintImpl(hi: hi, lo: lo)
 
-func copyMem*(x: UintImpl, ret: var openArray[byte]) {.compileTime.} =
-  const size = bitsof(x) div 8
-  type DT = type x.leastSignificantWord
-  for i in 0 ..< size:
-    ret[i] = x.getByte(i)
-
 func toBytes*(x: UintImpl, endian: Endianness = system.cpuEndian): auto {.inline.} =
   # TODO can't use bitsof in return type (compiler bug?), hence return auto
   var ret: array[bitsof(x) div 8, byte]
   when nimvm:
     if endian == system.cpuEndian:
-      copyMem(x, ret)
+      copyToArray(ret, x)
     else:
       let v = swapBytes(x)
-      copyMem(v, ret)
+      copyToArray(ret, v)
   else:
     if endian == system.cpuEndian:
       copyMem(addr ret[0], unsafeAddr x, ret.len)