diff --git a/vlib/builtin/prealloc.c.v b/vlib/builtin/prealloc.c.v
index b0feba6b34..0ef66fc650 100644
--- a/vlib/builtin/prealloc.c.v
+++ b/vlib/builtin/prealloc.c.v
@@ -13,8 +13,7 @@ module builtin
 // NB: `-prealloc` is NOT safe to be used for multithreaded programs!
 
 // size of the preallocated chunk
-// TODO: see why comptime calculation of integer expressions fails
-const prealloc_block_size = 16777216
+const prealloc_block_size = 16 * 1024 * 1024
 
 __global g_memory_block &VMemoryBlock
 [heap]
diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 115658c9a6..7692a4057d 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -213,6 +213,9 @@ pub:
 pub mut:
 	typ      Type      // the type of the const field, it can be any type in V
 	comments []Comment // comments before current const field
+	// the comptime_expr_value field is filled by the checker, when it has enough
+	// info to evaluate the constant at compile time
+	comptime_expr_value ComptTimeConstValue = empty_comptime_const_expr()
 }
 
 // const declaration
@@ -1098,16 +1101,18 @@ pub:
 // .in_prexpr is also needed because of that, because the checker needs to
 // show warnings about the deprecated C->V conversions `string(x)` and
 // `string(x,y)`, while skipping the real pointer casts like `&string(x)`.
+// 2021/07/17: TODO: since 6edfb2c, the above is fixed at the parser level,
+// we need to remove the hacks/special cases in vfmt and the checker too.
 pub struct CastExpr {
 pub:
 	arg Expr // `n` in `string(buf, n)`
 pub mut:
-	typ       Type // `string` TODO rename to `type_to_cast_to`
+	typ       Type   // `string`
+	expr      Expr   // `buf` in `string(buf, n)` and `&Type(buf)`
+	typname   string // `&Type` in `&Type(buf)`
+	expr_type Type   // `byteptr`, the type of the `buf` expression
+	has_arg   bool   // true for `string(buf, n)`, false for `&Type(buf)`
 	pos       token.Position
-	expr      Expr   // `buf` in `string(buf, n)`
-	typname   string // TypeSymbol.name
-	expr_type Type   // `byteptr`
-	has_arg   bool
 }
 
 pub struct AsmStmt {
diff --git a/vlib/v/ast/comptime_const_values.v b/vlib/v/ast/comptime_const_values.v
new file mode 100644
index 0000000000..e11571fe8b
--- /dev/null
+++ b/vlib/v/ast/comptime_const_values.v
@@ -0,0 +1,138 @@
+module ast
+
+pub type ComptTimeConstValue = EmptyExpr | byte | f64 | i64 | rune | string
+
+pub fn empty_comptime_const_expr() ComptTimeConstValue {
+	return EmptyExpr{}
+}
+
+pub fn (val ComptTimeConstValue) i64() ?i64 {
+	match val {
+		i64, byte {
+			return i64(val)
+		}
+		f64 {
+			if -9223372036854775808.0 <= val && val <= 9223372036854775807.0 {
+				return i64(val)
+			}
+			return none
+		}
+		string {
+			return val.i64()
+		}
+		rune {
+			return int(val)
+		}
+		EmptyExpr {
+			return none
+		}
+	}
+	return none
+}
+
+pub fn (val ComptTimeConstValue) int() ?int {
+	match val {
+		f64 {
+			if -2147483648.0 <= val && val <= 2147483647.0 {
+				return int(val)
+			}
+			return none
+		}
+		i64 {
+			if -2147483648 <= val && val <= 2147483647 {
+				return int(val)
+			}
+			return none
+		}
+		byte {
+			return int(val)
+		}
+		string {
+			return val.int()
+		}
+		rune {
+			return none
+		}
+		EmptyExpr {
+			return none
+		}
+	}
+	return none
+}
+
+pub fn (val ComptTimeConstValue) string() ?string {
+	match val {
+		i64, f64, byte {
+			return val.str()
+		}
+		string {
+			return val
+		}
+		rune {
+			return val.str()
+		}
+		EmptyExpr {
+			return none
+		}
+	}
+	return none
+}
+
+pub fn (val ComptTimeConstValue) f64() ?f64 {
+	match val {
+		f64 {
+			return val
+		}
+		i64, byte {
+			return f64(val)
+		}
+		string {
+			return val.f64()
+		}
+		rune {
+			return none
+		}
+		EmptyExpr {
+			return none
+		}
+	}
+	return none
+}
+
+pub fn (val ComptTimeConstValue) byte() ?byte {
+	match val {
+		byte {
+			return val
+		}
+		f64 {
+			if 0 <= val && val <= 255 {
+				return byte(val)
+			}
+			return none
+		}
+		i64 {
+			if 0 <= val && val <= 255 {
+				return byte(val)
+			}
+			return none
+		}
+		string {
+			x := val.int()
+			if 0 <= x && x <= 255 {
+				return byte(x)
+			}
+			return none
+		}
+		rune {
+			x := u32(val)
+			if 0 <= x && x <= 255 {
+				return byte(x)
+			}
+			return none
+		}
+		EmptyExpr {
+			return none
+		}
+	}
+	return none
+}
diff --git a/vlib/v/ast/str.v b/vlib/v/ast/str.v
index 2af805430b..7d54455b8a 100644
--- a/vlib/v/ast/str.v
+++ b/vlib/v/ast/str.v
@@ -358,6 +358,9 @@ pub fn (x Expr) str() string {
 			}
 			return s
 		}
+		SelectExpr {
+			return 'ast.SelectExpr'
+		}
 		SelectorExpr {
 			return '${x.expr.str()}.$x.field_name'
 		}
@@ -410,7 +413,50 @@ pub fn (x Expr) str() string {
 		None {
 			return 'none'
 		}
-		else {}
+		IsRefType {
+			return 'isreftype(' + if x.is_type {
+				global_table.type_to_str(x.typ)
+			} else {
+				x.expr.str()
+			} + ')'
+		}
+		IfGuardExpr {
+			return x.var_name + ' := ' + x.expr.str()
+		}
+		StructInit {
+			sname := global_table.get_type_symbol(x.typ).name
+			return '$sname{....}'
+		}
+		ArrayDecompose {
+			return 'ast.ArrayDecompose'
+		}
+		Assoc {
+			return 'ast.Assoc'
+		}
+		ChanInit {
+			return 'ast.ChanInit'
+		}
+		ComptimeCall {
+			return 'ast.ComptimeCall'
+		}
+		EmptyExpr {
+			return 'ast.EmptyExpr'
+		}
+		LockExpr {
+			return 'ast.LockExpr'
+		}
+		MatchExpr {
+			return 'ast.MatchExpr'
+		}
+		NodeError {
+			return 'ast.NodeError'
+		}
+		OrExpr {
+			return 'ast.OrExpr'
+		}
+		SqlExpr {
+			return 'ast.SqlExpr'
+		}
 	}
 	return '[unhandled expr type $x.type_name()]'
 }
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 213451f79f..6a8c54a889 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3608,10 +3608,13 @@ pub fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 	}
 	mut needs_order := false
 	mut done_fields := []int{}
-	for i, field in node.fields {
+	for i, mut field in node.fields {
 		c.const_decl = field.name
 		c.const_deps << field.name
 		typ := c.check_expr_opt_call(field.expr, c.expr(field.expr))
+		if ct_value := eval_comptime_const_expr(field.expr, 0) {
+			field.comptime_expr_value = ct_value
+		}
 		node.fields[i].typ = c.table.mktyp(typ)
 		for cd in c.const_deps {
 			for j, f in node.fields {
@@ -4345,7 +4348,7 @@ pub fn (mut c Checker) array_init(mut array_init ast.ArrayInit) ast.Type {
 	} else if array_init.is_fixed && array_init.exprs.len == 1
 		&& array_init.elem_type != ast.void_type {
 		// [50]byte
-		mut fixed_size := 0
+		mut fixed_size := i64(0)
 		init_expr := array_init.exprs[0]
 		c.expr(init_expr)
 		match init_expr {
@@ -4354,16 +4357,18 @@ pub fn (mut c Checker) array_init(mut array_init ast.ArrayInit) ast.Type {
 			}
 			ast.Ident {
 				if init_expr.obj is ast.ConstField {
-					if cint := eval_int_expr(init_expr.obj.expr, 0) {
-						fixed_size = cint
+					if comptime_value := eval_comptime_const_expr(init_expr.obj.expr,
+						0)
+					{
+						fixed_size = comptime_value.i64() or { fixed_size }
 					}
 				} else {
 					c.error('non-constant array bound `$init_expr.name`', init_expr.pos)
 				}
 			}
 			ast.InfixExpr {
-				if cint := eval_int_expr(init_expr, 0) {
-					fixed_size = cint
+				if comptime_value := eval_comptime_const_expr(init_expr, 0) {
+					fixed_size = comptime_value.i64() or { fixed_size }
 				}
 			}
 			else {
@@ -4373,7 +4378,7 @@ pub fn (mut c Checker) array_init(mut array_init ast.ArrayInit) ast.Type {
 		if fixed_size <= 0 {
 			c.error('fixed size cannot be zero or negative', init_expr.position())
 		}
-		idx := c.table.find_or_register_array_fixed(array_init.elem_type, fixed_size,
+		idx := c.table.find_or_register_array_fixed(array_init.elem_type, int(fixed_size),
 			init_expr)
 		if array_init.elem_type.has_flag(.generic) {
 			array_init.typ = ast.new_type(idx).set_flag(.generic)
@@ -4387,47 +4392,6 @@ pub fn (mut c Checker) array_init(mut array_init ast.ArrayInit) ast.Type {
 	return array_init.typ
 }
 
-fn eval_int_expr(expr ast.Expr, nlevel int) ?int {
-	if nlevel > 100 {
-		// protect against a too deep comptime eval recursion:
-		return none
-	}
-	match expr {
-		ast.IntegerLiteral {
-			return expr.val.int()
-		}
-		ast.InfixExpr {
-			left := eval_int_expr(expr.left, nlevel + 1) ?
-			right := eval_int_expr(expr.right, nlevel + 1) ?
-			match expr.op {
-				.plus { return left + right }
-				.minus { return left - right }
-				.mul { return left * right }
-				.div { return left / right }
-				.mod { return left % right }
-				.xor { return left ^ right }
-				.pipe { return left | right }
-				.amp { return left & right }
-				.left_shift { return left << right }
-				.right_shift { return left >> right }
-				else { return none }
-			}
-		}
-		ast.Ident {
-			if expr.obj is ast.ConstField {
-				// an int constant?
-				cint := eval_int_expr(expr.obj.expr, nlevel + 1) ?
-				return cint
-			}
-		}
-		else {
-			// dump(expr)
-			return none
-		}
-	}
-	return none
-}
-
 [inline]
 fn (mut c Checker) check_loop_label(label string, pos token.Position) {
 	if label.len == 0 {
diff --git a/vlib/v/checker/comptime_const_eval.v b/vlib/v/checker/comptime_const_eval.v
new file mode 100644
index 0000000000..d514e08a97
--- /dev/null
+++ b/vlib/v/checker/comptime_const_eval.v
@@ -0,0 +1,94 @@
+module checker
+
+import v.ast
+
+fn eval_comptime_const_expr(expr ast.Expr, nlevel int) ?ast.ComptTimeConstValue {
+	if nlevel > 100 {
+		// protect against a too deep comptime eval recursion
+		return none
+	}
+	x := expr
+	match expr {
+		ast.IntegerLiteral {
+			return expr.val.i64()
+		}
+		ast.StringLiteral {
+			return expr.val
+		}
+		ast.CastExpr {
+			cast_expr_value := eval_comptime_const_expr(expr.expr, nlevel + 1) or { return none }
+			if expr.typ == ast.byte_type {
+				return cast_expr_value.byte() or { return none }
+			}
+			if expr.typ == ast.int_type {
+				match cast_expr_value {
+					byte {
+						eprintln('>>>>>>> byte cast_expr_value: $cast_expr_value | x: $x')
+						return i64(cast_expr_value)
+					}
+					i64 {
+						eprintln('>>>>>>> i64 cast_expr_value: $cast_expr_value | x: $x')
+						if int_min <= cast_expr_value && cast_expr_value <= int_max {
+							return i64(cast_expr_value)
+						}
+					}
+					else {}
+				}
+				return none
+			}
+		}
+		ast.InfixExpr {
+			left := eval_comptime_const_expr(expr.left, nlevel + 1) ?
+			right := eval_comptime_const_expr(expr.right, nlevel + 1) ?
+			if left is string && right is string {
+				match expr.op {
+					.plus {
+						return left + right
+					}
+					else {
+						return none
+					}
+				}
+			} else if left is i64 && right is i64 {
+				match expr.op {
+					.plus { return left + right }
+					.minus { return left - right }
+					.mul { return left * right }
+					.div { return left / right }
+					.mod { return left % right }
+					.xor { return left ^ right }
+					.pipe { return left | right }
+					.amp { return left & right }
+					.left_shift { return left << right }
+					.right_shift { return left >> right }
+					else { return none }
+				}
+			} else if left is byte && right is byte {
+				match expr.op {
+					.plus { return left + right }
+					.minus { return left - right }
+					.mul { return left * right }
+					.div { return left / right }
+					.mod { return left % right }
+					.xor { return left ^ right }
+					.pipe { return left | right }
+					.amp { return left & right }
+					.left_shift { return left << right }
+					.right_shift { return left >> right }
+					else { return none }
+				}
+			}
+		}
+		ast.Ident {
+			if expr.obj is ast.ConstField {
+				// an existing constant?
+				return eval_comptime_const_expr(expr.obj.expr, nlevel + 1)
+			}
+		}
+		else {
+			// eprintln('>>> nlevel: $nlevel | another $expr.type_name() | $expr ')
+			return none
+		}
+	}
+	return none
+}
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 6d6208198e..b7280eb044 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4846,24 +4846,7 @@ fn (mut g Gen) const_decl(node ast.ConstDecl) {
 				continue
 			}
 		}
-
 		name := c_name(field.name)
-		/*
-		if field.typ == ast.byte_type {
-			g.const_decl_simple_define(name, val)
-			return
-		}
-		*/
-		/*
-		if ast.is_number(field.typ) {
-			g.const_decl_simple_define(name, val)
-		} else if field.typ == ast.string_type {
-			g.definitions.writeln('string _const_$name; // a string literal, inited later')
-			if g.pref.build_mode != .build_module {
-				g.stringliterals.writeln('\t_const_$name = $val;')
-			}
-		} else {
-		*/
 		field_expr := field.expr
 		match field.expr {
 			ast.ArrayInit {
@@ -4895,6 +4878,11 @@ fn (mut g Gen) const_decl(node ast.ConstDecl) {
 				}
 			}
 			else {
+				if ct_value := comptime_expr_value(field) {
+					if g.const_decl_precomputed(field.mod, name, ct_value, field.typ) {
+						continue
+					}
+				}
 				if is_simple_define_const(field) {
 					// "Simple" expressions are not going to need multiple statements,
 					// only the ones which are inited later, so it's safe to use expr_string
@@ -4907,6 +4895,15 @@ fn (mut g Gen) const_decl(node ast.ConstDecl) {
 	}
 }
 
+fn comptime_expr_value(obj ast.ScopeObject) ?ast.ComptTimeConstValue {
+	if obj is ast.ConstField {
+		if obj.comptime_expr_value !is ast.EmptyExpr {
+			return obj.comptime_expr_value
+		}
+	}
+	return none
+}
+
 fn is_simple_define_const(obj ast.ScopeObject) bool {
 	if obj is ast.ConstField {
 		return match obj.expr {
@@ -4917,6 +4914,38 @@ fn is_simple_define_const(obj ast.ScopeObject) bool {
 	return false
 }
 
+fn (mut g Gen) const_decl_precomputed(mod string, name string, ct_value ast.ComptTimeConstValue, typ ast.Type) bool {
+	mut styp := g.typ(typ)
+	cname := '_const_$name'
+	// eprintln('>> cname: $cname | styp: $styp | $ct_value.type_name() | $ct_value')
+	match ct_value {
+		byte {
+			g.const_decl_write_precomputed(styp, cname, ct_value.str())
+		}
+		rune {
+			g.const_decl_write_precomputed(styp, cname, ct_value.str())
+		}
+		i64 {
+			g.const_decl_write_precomputed(styp, cname, ct_value.str())
+		}
+		f64 {
+			g.const_decl_write_precomputed(styp, cname, ct_value.str())
+		}
+		string {
+			escaped_val := util.smart_quote(ct_value, false)
+			g.const_decl_write_precomputed(styp, cname, '_SLIT("$escaped_val")')
+		}
+		ast.EmptyExpr {
+			return false
+		}
+	}
+	return true
+}
+
+fn (mut g Gen) const_decl_write_precomputed(styp string, cname string, ct_value string) {
+	g.definitions.writeln('$styp $cname = $ct_value; // precomputed')
+}
+
 fn (mut g Gen) const_decl_simple_define(name string, val string) {
 	// Simple expressions should use a #define
 	// so that we don't pollute the binary with unnecessary global vars
diff --git a/vlib/v/gen/c/cheaders.v b/vlib/v/gen/c/cheaders.v
index 5a3d71bfdd..8b3e228d75 100644
--- a/vlib/v/gen/c/cheaders.v
+++ b/vlib/v/gen/c/cheaders.v
@@ -179,7 +179,7 @@ const c_common_macros = '
 	#  define VNORETURN _Noreturn
 	# elif defined(__GNUC__) && __GNUC__ >= 2
 	#  define VNORETURN __attribute__((noreturn))
-	# endif	
+	# endif
 	#ifndef VNORETURN
 		#define VNORETURN
 	#endif
@@ -191,7 +191,7 @@ const c_common_macros = '
 		#if (V_GCC_VERSION >= 40500L)
 			#define VUNREACHABLE()  do { __builtin_unreachable(); } while (0)
 		#endif
-	#endif		
+	#endif
 	#if defined(__clang__) && defined(__has_builtin)
 		#if __has_builtin(__builtin_unreachable)
 			#define VUNREACHABLE()  do { __builtin_unreachable(); } while (0)
@@ -199,7 +199,7 @@ const c_common_macros = '
 	#endif
 	#ifndef VUNREACHABLE
 		#define VUNREACHABLE() do { } while (0)
-	#endif		
+	#endif
 #endif
 
 //likely and unlikely macros
@@ -232,13 +232,17 @@ static inline bool _us64_lt(uint64_t a, int64_t b) { return a < INT64_MAX && (in
 const c_helper_macros = '//============================== HELPER C MACROS =============================*/
 // _SLIT0 is used as NULL string for literal arguments
 // `"" s` is used to enforce a string literal argument
-#define _SLIT0 (string){.len=0}
+#define _SLIT0 (string){.str=(byteptr)(""), .len=0, .is_lit=1}
 #define _SLIT(s) ((string){.str=(byteptr)("" s), .len=(sizeof(s)-1), .is_lit=1})
+#define _SLEN(s, n) ((string){.str=(byteptr)("" s), .len=n, .is_lit=1})
+
 // take the address of an rvalue
 #define ADDR(type, expr) (&((type[]){expr}[0]))
+
 // copy something to the heap
 #define HEAP(type, expr) ((type*)memdup((void*)&((type[]){expr}[0]), sizeof(type)))
 #define HEAP_noscan(type, expr) ((type*)memdup_noscan((void*)&((type[]){expr}[0]), sizeof(type)))
+
 #define _PUSH_MANY(arr, val, tmp, tmp_typ) {tmp_typ tmp = (val); array_push_many(arr, tmp.data, tmp.len);}
 #define _PUSH_MANY_noscan(arr, val, tmp, tmp_typ) {tmp_typ tmp = (val); array_push_many_noscan(arr, tmp.data, tmp.len);}
 '