diff --git a/src/test.cpp b/src/test.cpp
index fa44bf4..26a9ea3 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -223,7 +223,7 @@ namespace {
 // treats numbers as [0-9.]+. May stack overflow on deeply nested json documents
 struct Parser1 {
   Parser1(char *buf, int len, const Callbacks *callbacks, void *data)
-      : buf(buf), len(len), callbacks(callbacks), data(data) {}
+      : buf(buf), bufEnd(buf + len), callbacks(callbacks), data(data) {}
 
   // Returns false to reject
   [[nodiscard]] bool parse() { return parse_element(); }
@@ -235,29 +235,29 @@ struct Parser1 {
 
 private:
   char *buf;
-  int len;
+  char *bufEnd;
   const Callbacks *const callbacks;
   void *const data;
 
+  int len() const { return bufEnd - buf; }
+
   // Helpers
   void maybeSkipWs() {
-    int leadingWs = leadingWhitespaceCount(buf, len);
+    int leadingWs = leadingWhitespaceCount(buf, len());
     buf += leadingWs;
-    len -= leadingWs;
   }
   bool parseLiteral(const char *literal) {
     const int litLen = strlen(literal);
-    if (len < litLen) {
+    if (len() < litLen) {
       return false;
     }
-    len -= litLen;
     return memcmp(std::exchange(buf, buf + litLen), literal, litLen) == 0;
   }
 
   // functions corresponding to productions
   bool parse_element() {
     maybeSkipWs();
-    if (len == 0) {
+    if (len() == 0) {
       return false;
     }
     if (*buf == '{') {
@@ -299,7 +299,7 @@ private:
     }
     callbacks->on_begin_object(data);
     maybeSkipWs();
-    if (len == 0) {
+    if (len() == 0) {
       return false;
     }
     if (*buf != '}') {
@@ -318,7 +318,7 @@ private:
     if (!parse_member()) {
       return false;
     }
-    if (len == 0) {
+    if (len() == 0) {
       return false;
     }
     if (*buf == ',') {
@@ -351,7 +351,7 @@ private:
     }
     callbacks->on_begin_array(data);
     maybeSkipWs();
-    if (len == 0) {
+    if (len() == 0) {
       return false;
     }
     if (*buf != ']') {
@@ -371,7 +371,7 @@ private:
     if (!parse_element()) {
       return false;
     }
-    if (len == 0) {
+    if (len() == 0) {
       return false;
     }
     if (*buf == ',') {
@@ -388,14 +388,13 @@ private:
     if (!parseLiteral("\"")) {
       return false;
     }
-    auto *result = (char *)memchr(buf, '"', len);
+    auto *result = (char *)memchr(buf, '"', len());
     if (result == nullptr) {
       return false;
     }
     int stringLen = result - buf;
     callbacks->on_string_data(data, buf, stringLen);
     buf += stringLen;
-    len -= stringLen;
     if (!parseLiteral("\"")) {
       return false;
     }
@@ -407,12 +406,11 @@ private:
     callbacks->on_begin_number(data);
     char *const bufBefore = buf;
     for (;;) {
-      if (len == 0) {
+      if (len() == 0) {
         return false;
       }
       if ('0' <= *buf && *buf <= '9' || (*buf == '.')) {
         ++buf;
-        --len;
       } else {
         break;
       }
@@ -464,7 +462,7 @@ private:
 // [0-9.]+. Could be adapted to have a streaming interface. Uses O(1) memory.
 struct Parser2 {
   Parser2(char *buf, int len, const Callbacks *callbacks, void *data)
-      : buf(buf), len(len), callbacks(callbacks), data(data) {}
+      : buf(buf), bufEnd(buf + len), callbacks(callbacks), data(data) {}
 
   // Returns false to reject
   [[nodiscard]] bool parse() {
@@ -484,17 +482,16 @@ struct Parser2 {
 private:
   // Helpers
   void maybeSkipWs() {
-    int leadingWs = leadingWhitespaceCount(buf, len);
+    int leadingWs = leadingWhitespaceCount(buf, len());
+    // printf("ws: %d\n", leadingWs);
     buf += leadingWs;
-    len -= leadingWs;
   }
   bool parseLiteral(const char *literal) {
     const int litLen = strlen(literal);
-    if (len < litLen) {
+    if (len() < litLen) {
       return false;
     }
     if (memcmp(buf, literal, litLen) == 0) {
-      len -= litLen;
       buf += litLen;
       return true;
     }
@@ -502,16 +499,14 @@ private:
   }
   bool parse_number() {
     char *const bufBefore = buf;
-    if (len == 0 || !('0' <= *buf && *buf <= '9' || (*buf == '.'))) {
+    if (len() == 0 || !('0' <= *buf && *buf <= '9' || (*buf == '.'))) {
       return false;
     }
     callbacks->on_begin_number(data);
     ++buf;
-    --len;
     for (;;) {
       if ('0' <= *buf && *buf <= '9' || (*buf == '.')) {
         ++buf;
-        --len;
       } else {
         break;
       }
@@ -528,14 +523,13 @@ private:
       return false;
     }
     callbacks->on_begin_string(data);
-    auto *result = (char *)memchr(buf, '"', len);
+    auto *result = (char *)memchr(buf, '"', len());
     if (result == nullptr) {
       return false;
     }
     int stringLen = result - buf;
     callbacks->on_string_data(data, buf, stringLen);
     buf += stringLen;
-    len -= stringLen;
     if (!parseLiteral("\"")) {
       return false;
     }
@@ -650,7 +644,8 @@ private:
   };
 
   char *buf;
-  int len;
+  char *bufEnd;
+  int len() { return bufEnd - buf; }
   const Callbacks *const callbacks;
   void *const data;
   Symbol stack[kMaxStackSize];