[mycpp] MaybeShrink() replaces SetObjLenFromStrLen()

It will also be used for SmallStr.

cpp/core.cc

@@ -38,7 +38,7 @@ Tuple2<int, int> Read(int fd, int n, List<Str*>* chunks) {
   }
 
   // Now we know how much data we got back
-  s->SetObjLenFromStrLen(length);
+  s->MaybeShrink(length);
   chunks->append(s);
 
   return Tuple2<int, int>(length, 0);
@@ -296,7 +296,7 @@ Str* BackslashEscape(Str* s, Str* meta_chars) {
     }
     *p++ = c;
   }
-  buf->SetObjLenFromStrLen(p - buf->data_);
+  buf->MaybeShrink(p - buf->data_);
   return buf;
 }
 

cpp/libc.cc

@@ -20,7 +20,7 @@ Str* gethostname() {
     throw Alloc<OSError>(errno);
   }
   // Important: set the length of the string!
-  result->SetObjLenFromC();
+  result->MaybeShrink(strlen(result->data_));
   return result;
 }
 

cpp/qsn.h

@@ -47,7 +47,7 @@ inline Str* UEscape(int codepoint) {
   // 1 for }
   Str* result = OverAllocatedStr(10);
   int n = sprintf(result->data(), "\\u{%x}", codepoint);
-  result->SetObjLenFromStrLen(n);  // truncate to what we wrote
+  result->MaybeShrink(n);  // truncate to what we wrote
   return result;
 }
 

cpp/stdlib.cc

@@ -167,7 +167,7 @@ Str* strftime(Str* s, time_t ts) {
     // No error location info, but leaving it out points reliably to 'printf'
     e_die(StrFromC("strftime() result exceeds 1024 bytes"));
   }
-  result->SetObjLenFromStrLen(n);
+  result->MaybeShrink(n);
   return result;
 }
 

cpp/stdlib.h

@@ -33,7 +33,7 @@ inline Str* getcwd() {
     throw Alloc<OSError>(errno);
   }
   // Important: set the length of the string!
-  result->SetObjLenFromC();
+  result->MaybeShrink(strlen(result->data_));
   return result;
 }
 

mycpp/gc_builtins.cc

@@ -22,7 +22,7 @@ void println_stderr(Str* s) {
 Str* str(int i) {
   Str* s = OverAllocatedStr(kIntBufSize);
   int length = snprintf(s->data(), kIntBufSize, "%d", i);
-  s->SetObjLenFromStrLen(length);
+  s->MaybeShrink(length);
   return s;
 }
 

mycpp/gc_mylib.cc

@@ -204,7 +204,7 @@ Str* BufWriter::getvalue() {
     return kEmptyString;
   } else {
     Str* s = str_;
-    s->SetObjLenFromStrLen(len_);
+    s->MaybeShrink(len_);
     str_ = nullptr;
     len_ = -1;
     return s;

mycpp/gc_str.h

@@ -14,12 +14,8 @@ class Str {
     return data_;
   }
 
-  void SetObjLenFromStrLen(int str_len);
-
-  // Useful for getcwd() + PATH_MAX, gethostname() + HOSTNAME_MAX, etc.
-  void SetObjLenFromC() {
-    SetObjLenFromStrLen(strlen(data_));
-  }
+  // Call this after writing into buffer created by OverAllocatedStr()
+  void MaybeShrink(int str_len);
 
   Str* index_(int i);
 
@@ -83,15 +79,23 @@ class Str {
 
 constexpr int kStrHeaderSize = offsetof(Str, data_);
 
-inline void Str::SetObjLenFromStrLen(int str_len) {
-  // header_.obj_len = kStrHeaderSize + str_len + 1;
+// Note: for SmallStr, we might copy into the VALUE
+inline void Str::MaybeShrink(int str_len) {
+#ifdef MARK_SWEEP
   STR_LEN(header_) = str_len;
+#else
+  // reversed in len() to derive string length
+  header_.obj_len = kStrHeaderSize + str_len + 1;
+#endif
 }
 
 inline int len(const Str* s) {
-  // DCHECK(s->header_.obj_len >= kStrHeaderSize - 1);
-  // return s->header_.obj_len - kStrHeaderSize - 1;
+#ifdef MARK_SWEEP
   return STR_LEN(s->header_);
+#else
+  DCHECK(s->header_.obj_len >= kStrHeaderSize - 1);
+  return s->header_.obj_len - kStrHeaderSize - 1;
+#endif
 }
 
 // Notes:
@@ -112,7 +116,12 @@ inline Str* NewStr(int len) {
   void* place = gHeap.Allocate(obj_len);
 
   auto s = new (place) Str();
+#ifdef MARK_SWEEP
   STR_LEN(s->header_) = len;
+#else
+  // reversed in len() to derive string length
+  header_.obj_len = kStrHeaderSize + str_len + 1;
+#endif
   return s;
 }
 

mycpp/gc_str_test.cc

@@ -91,7 +91,7 @@ TEST test_str_creation() {
   // Hm annoying that we have to do a const_cast
   memcpy(s4->data(), "foo", 3);
   strcpy(s4->data(), "foo");
-  s4->SetObjLenFromStrLen(3);
+  s4->MaybeShrink(3);
 
   ASSERT_EQ(3, len(s4));
   ASSERT_EQ(0, strcmp("foo", s4->data_));