untested rewrite of stretchy_buffer relying on implicit cast from void*

stretchy_buffer.h

@@ -1,28 +1,142 @@
-// stretchy buffer // init: NULL // free: sbfree() // push_back: sbpush() // size: sbcount() //
-#define stbcg_sbfree(a)         ((a) ? free(stb__sbraw(a)),0 : 0)
-#define stbcg_sbpush(a,v)       (stb__sbmaybegrow(a,1), (a)[stb__sbn(a)++] = (v))
-#define stbcg_sbcount(a)        ((a) ? stb__sbn(a) : 0)
-#define stbcg_sbadd(a,n)        (stb__sbmaybegrow(a,n), stb__sbn(a)+=(n), &(a)[stb__sbn(a)-(n)])
-#define stbcg_sblast(a)         ((a)[stb__sbn(a)-1])
+// stretchy_buffer.h - v0.9 - public domain
+// a vector<>-like dynamic array for C
+//
+// version history:
+//      0.9 -  rewrite to try to avoid strict-aliasing optimization
+//             issues, but won't compile as C++
+//
+// The idea:
+//
+//    This implements an approximation to C++ vector<> for C, in that it
+//    provides a generic definition for dynamic arrays which you can
+//    still access in a typesafe way using arr[i] or *(arr+i). However,
+//    it is simply a convenience wrapper around the common idiom of
+//    of keeping a set of variables (in a struct or globals) which store
+//        - pointer to array
+//        - the length of the "in-use" part of the array
+//        - the current size of the allocated array
+//
+//    I find it to be super-convenient in C, but it lacks many of the
+//    abilities of vector<>: there is no range checking, the object
+//    address isn't stable (see next section for details), the set
+//    of methods available is small (although the file stb.h has
+//    another implementation of stretchy buffers called 'stb_arr'
+//    which provides more methods, e.g. for insertion and deletion).
+//
+// How to use:
+//
+//    Unlike other stb header file libraries, there is no need to
+//    define an _IMPLEMENTATION symbol. Every #include creates as
+//    much implementation is needed.
+//
+//    stretchy_buffer.h does not define any types, so you do not
+//    need to #include it to before defining data types that are
+//    stretchy buffers, only in files that *manipulate* stretchy
+//    buffers.
+//
+//    If you want a stretchy buffer aka dynamic array containing
+//    objects of TYPE, declare such an array as:
+//
+//       TYPE *myarray = NULL;
+//
+//    (There is no typesafe way to distinguish between stretchy
+//    buffers and regular arrays/pointers; this is necessary to
+//    make ordinary array indexing work on these objects.)
+//
+//    Unlike C++ vector<>, the stretchy_buffer has the same
+//    semantics as an object that you manually malloc and realloc.
+//    The pointer may relocate every time you add a new object
+//    to it, so you:
+//
+//         1. can't take long-term pointers to elements of the array
+//         2. have to return the pointer from functions which might expand it
+//            (either as a return value or by passing it back)
+//
+//    Now you can do the following things with this array:
+//
+//         sb_free(TYPE *a)           free the array
+//         sb_count(TYPE *a)          the number of elements in the array
+//         sb_push(TYPE *a, TYPE v)   adds v on the end of the array, a la push_back
+//         sb_add(TYPE *a, int n)     adds n uninitialized elements at end of array & returns pointer to first added
+//         sb_last(TYPE *a)           returns an lvalue of the last item in the array
+//         a[2]                       access the 2nd (counting from 0) element of the array
+//
+//     #define STRETCHY_BUFFER_NO_SHORT_NAMES to only export
+//     names of the form 'stb_sb_' if you have a name that would
+//     otherwise collide.
+//
+//     Note that these are all macros and many of them evaluate
+//     their arguments more than once, so the arguments should
+//     be side-effect-free.
+//
+//     Note that 'TYPE *a' in sb_push and sb_add must be lvalues
+//     so that the library can overwrite the existing pointer if
+//     the object has to be reallocated.
+//
+//     In an out-of-memory condition, the code will try to
+//     set up a null-pointer or otherwise-invalid-pointer
+//     exception to happen later. It's possible optimizing
+//     compilers could detect this write-to-null statically
+//     and optimize away some of the code, but it should only
+//     be along the failure path. Nevertheless, for more security
+//     in the face of such compilers, #define STRETCHY_BUFFER_OUT_OF_MEMORY
+//     to a statement such as assert(0) or exit(1) or something
+//     to force a failure when out-of-memory occurs.
+//
+// How it works:
+//
+//    A long-standing tradition in things like malloc implementations
+//    is to store extra data before the beginning of the block returned
+//    to the user. The stretchy buffer implementation here uses the
+//    same trick; the current-count and current-allocation-size are
+//    stored before the beginning of the array returned to the user.
+//    (This means you can't directly free() the pointer, because the
+//    allocated pointer is different from the type-safe pointer provided
+//    to the user.)
+//
+//    The details are trivial and implementation is straightforward;
+//    the main trick is in realizing in the first place that it's
+//    possible to do this in a generic, type-safe way in C.
+
+#ifndef NO_STRETCHY_BUFFER_SHORT_NAMES
+#define sb_free   stb_sb_free
+#define sb_push   stb_sb_push
+#define sb_count  stb_sb_count
+#define sb_add    stb_sb_add
+#define sb_last   stb_sb_last
+#endif
+
+#define stb_sb_free(a)         ((a) ? free(stb__sbraw(a)),0 : 0)
+#define stb_sb_push(a,v)       (stb__sbmaybegrow(a,1), (a)[stb__sbn(a)++] = (v))
+#define stb_sb_count(a)        ((a) ? stb__sbn(a) : 0)
+#define stb_sb_add(a,n)        (stb__sbmaybegrow(a,n), stb__sbn(a)+=(n), &(a)[stb__sbn(a)-(n)])
+#define stb_sb_last(a)         ((a)[stb__sbn(a)-1])
 
-#include <stdlib.h>
 #define stb__sbraw(a) ((int *) (a) - 2)
 #define stb__sbm(a)   stb__sbraw(a)[0]
 #define stb__sbn(a)   stb__sbraw(a)[1]
 
-#define stb__sbneedgrow(a,n)  ((a)==0 || stb__sbn(a)+n >= stb__sbm(a))
+#define stb__sbneedgrow(a,n)  ((a)==0 || stb__sbn(a)+(n) >= stb__sbm(a))
 #define stb__sbmaybegrow(a,n) (stb__sbneedgrow(a,(n)) ? stb__sbgrow(a,n) : 0)
-#define stb__sbgrow(a,n)  stb__sbgrowf((void **) &(a), (n), sizeof(*(a)))
+#define stb__sbgrow(a,n)      ((a) = stb__sbgrowf((a), (n), sizeof(*(a))))
 
-static void stb__sbgrowf(void **arr, int increment, int itemsize)
+#include <stdlib.h>
+
+static void * stb__sbgrowf(void *arr, int increment, int itemsize)
 {
-   int d = *arr ? 2*stb__sbm(*arr) : 0, n2 = stbcg_sbcount(*arr) + increment;
-   int m = d > n2 ? d : n2;
-   void *p = realloc(*arr ? stb__sbraw(*arr) : 0, itemsize * m + sizeof(int)*2);
-   assert(p);
+   int dbl_cur = arr ? 2*stb__sbm(arr) : 0;
+   int min_needed = stb_sb_count(arr) + increment;
+   int m = dbl_cur > min_needed ? dbl_cur : min_needed;
+   int *p = realloc(arr ? stb__sbraw(arr) : 0, itemsize * m + sizeof(int)*2);
    if (p) {
-      if (!*arr) ((int *) p)[1] = 0;
-      *arr = (void *) ((int *) p + 2);
-      stb__sbm(*arr) = m;
+      if (!arr)
+         p[1] = 0;
+      p[0] = m;
+      return p;
+   } else {
+      #ifdef STRETCHY_BUFFER_OUT_OF_MEMORY
+      STRETCHY_BUFFER_OUT_OF_MEMORY ;
+      #endif
+      return (void *) 8; // try to force a NULL pointer exception later
    }
 }

tests/stb.dsp

@@ -102,6 +102,10 @@ SOURCE=..\stb_vorbis.c
 # End Source File
 # Begin Source File
 
+SOURCE=.\stretchy_buffer_test.c
+# End Source File
+# Begin Source File
+
 SOURCE=.\test_truetype.c
 # End Source File
 # Begin Source File

tests/stretchy_buffer_test.c

@@ -0,0 +1 @@
+#include "stretchy_buffer.h"