WIP: improve Int.format performance

Author: yorickpeterse

std/src/std/int.inko

@@ -14,7 +14,7 @@ import std.ops (
   ShiftRight, Subtract, UnsignedShiftRight,
 )
 import std.range (ExclusiveRange, InclusiveRange)
-import std.string (ToString)
+import std.string (PrimitiveString, ToString)
 
 fn extern inko_int_checked_pow(left: Int, right: Int) -> CheckedIntResult
 
@@ -74,6 +74,74 @@ type pub copy enum Format {
   }
 }
 
+type extern Buffer {
+  let @0: Uint8
+  let @1: Uint8
+  let @2: Uint8
+  let @3: Uint8
+  let @4: Uint8
+  let @5: Uint8
+  let @6: Uint8
+  let @7: Uint8
+  let @8: Uint8
+  let @9: Uint8
+  let @10: Uint8
+  let @11: Uint8
+  let @12: Uint8
+  let @13: Uint8
+  let @14: Uint8
+  let @15: Uint8
+  let @16: Uint8
+  let @17: Uint8
+  let @18: Uint8
+  let @19: Uint8
+  let @20: Uint8
+  let @21: Uint8
+  let @22: Uint8
+  let @23: Uint8
+  let @24: Uint8
+  let @25: Uint8
+  let @26: Uint8
+  let @27: Uint8
+  let @28: Uint8
+  let @29: Uint8
+  let @30: Uint8
+  let @31: Uint8
+  let @32: Uint8
+  let @33: Uint8
+  let @34: Uint8
+  let @35: Uint8
+  let @36: Uint8
+  let @37: Uint8
+  let @38: Uint8
+  let @39: Uint8
+  let @40: Uint8
+  let @41: Uint8
+  let @42: Uint8
+  let @43: Uint8
+  let @44: Uint8
+  let @45: Uint8
+  let @46: Uint8
+  let @47: Uint8
+  let @48: Uint8
+  let @49: Uint8
+  let @50: Uint8
+  let @51: Uint8
+  let @52: Uint8
+  let @53: Uint8
+  let @54: Uint8
+  let @55: Uint8
+  let @56: Uint8
+  let @57: Uint8
+  let @58: Uint8
+  let @59: Uint8
+  let @60: Uint8
+  let @61: Uint8
+  let @62: Uint8
+  let @63: Uint8
+  let @64: Uint8
+}
+
 # A 64-bits signed integer type.
 #
 # `Int` values can represent values in the range
@@ -266,6 +334,50 @@ type builtin Int {
     bytes.into_string
   }
 
+  # TODO
+  fn pub format_fast(format: Format) -> String {
+    let base = format.to_base
+
+    match self {
+      case 0 -> return '0'
+      # MIN can't be turned positive using absolute(), so we have to handle
+      # these cases explicitly.
+      case MIN if base == 2 -> {
+        return '-1000000000000000000000000000000000000000000000000000000000000000'
+      }
+      case MIN if base == 10 -> return '-9223372036854775808'
+      case MIN if base == 16 -> return '-8000000000000000'
+      case _ -> {}
+    }
+
+    let alphabet = '0123456789abcdef'
+    let bytes = Buffer()
+    let mut int = absolute
+    let mut idx = 64
+    let mut len = 1
+
+    while int > 0 {
+      let ptr = (mut bytes) as Int + idx as Pointer[Uint8]
+
+      ptr.0 = alphabet.get(int % base).or_panic as Uint8
+      int /= base
+      len += 1
+      idx -= 1
+    }
+
+    if self < 0 {
+      len += 1
+      ((mut bytes) as Int + idx as Pointer[Uint8]).0 = 0x2D as Uint8
+    }
+
+    String.from_borrowed_primitive(
+      PrimitiveString(
+        bytes: (mut bytes) as Int + idx as Pointer[Uint8],
+        size: len,
+      ),
+    )
+  }
+
   # Calls the supplied closure `self` times.
   #
   # # Examples