Took a ptrmath macro from nim forum

Author: CodeDoes

nimspice/ptrmath.nim

@@ -0,0 +1,35 @@
+## https://forum.nim-lang.org/t/1188#7366
+## https://forum.nim-lang.org/t/1188#7374
+## https://forum.nim-lang.org/t/1188#17709
+template ptrMath*(body: untyped) =
+  template `+`[T](p: ptr T, off: SomeInteger): ptr T =
+    # cast[ptr type(p[])](cast[ByteAddress](p) +% off * sizeof(p[]))
+    cast[ptr T](cast[ByteAddress](p) +% off * sizeof(T))
+  
+  template `+=`[T](p: ptr T, off: SomeInteger) =
+    p = p + off
+  
+  template `-`[T](p: ptr T, off: SomeInteger): ptr T =
+    # cast[ptr type(p[])](cast[ByteAddress](p) -% off * sizeof(p[]))
+    cast[ptr T](cast[ByteAddress](p) -% off * sizeof(T))
+  
+  template `-=`[T](p: ptr T, off: SomeInteger) =
+    p = p - off
+  
+  template `[]`[T](p: ptr T, off: SomeInteger): T =
+    (p + off)[]
+  
+  template `[]=`[T](p: ptr T, off: SomeInteger, val: T) =
+    (p + off)[] = val
+  
+  body
+
+when isMainModule:
+  ptrMath:
+    var a: array[0..3, int]
+    for i in a.low..a.high:
+      a[i] += i
+    var p = addr(a[0])
+    p += 1
+    p[0] -= 2
+    echo p[0], " ", p[1]