cache functions per V8 polymorphic cache rules

lib/levels.js

@@ -57,6 +57,25 @@ function getLevelVal () {
   return this[levelValSym]
 }
 
+const loggingMethods = {
+  [levels.fatal]: {method: genLog(levels.fatal), count: 0},
+  [levels.error]: {method: genLog(levels.error), count: 0},
+  [levels.warn]: {method: genLog(levels.warn), count: 0},
+  [levels.info]: {method: genLog(levels.info), count: 0},
+  [levels.debug]: {method: genLog(levels.debug), count: 0},
+  [levels.trace]: {method: genLog(levels.trace), count: 0}
+}
+
+function getLoggingMethod (value) {
+  if (!(value in loggingMethods)) {
+    loggingMethods[value] = {method: genLog(value), count: 0}
+    return loggingMethods[value].method
+  }
+  loggingMethods[value].count = (loggingMethods[value].count + 1) % 4
+  if (loggingMethods[value].count === 0) loggingMethods[value].method = genLog(value)
+  return loggingMethods[value].method
+}
+
 function setLevelVal (num) {
   if (typeof num === 'string') return this[setLevelSym](num)
 
@@ -79,7 +98,7 @@ function setLevelVal (num) {
       this[key] = noop
       continue
     }
-    this[key] = genLog(values[key])
+    this[key] = getLoggingMethod(values[key])
   }
 }