Reference-counted copy-on-write JSON library.

Comes with tests and, presumably, bugs.

c/Makefile

@@ -1,4 +1,4 @@
-CC=gcc -Wall -std=gnu99 -ggdb
+CC=gcc -Wall -std=gnu99 -ggdb -Wno-unused-function
 
 .PHONY: all clean
 all: parsertest
@@ -19,3 +19,13 @@ parser.tab.h: parser.tab.c
 
 parsertest: parser.tab.c lexer.yy.c main.c opcode.c bytecode.c compile.c execute.c builtin.c
 	$(CC) -o $@ $^ -ljansson
+
+jvtest: jvtest.c jv.c jv_print.c
+	$(CC) -o $@ $^ -ljansson
+
+test: jvtest
+	valgrind --error-exitcode=1 -q --leak-check=full ./jvtest
+
+jsparse: jsparse.l jv.c
+	flex -o jsparse.c jsparse.l
+	gcc -o jsparse jsparse.c -ljansson

c/jv.c

@@ -0,0 +1,764 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "jv.h"
+
+/*
+ * Internal refcounting helpers
+ */
+
+static void jvp_refcnt_init(jv_complex* c) {
+  c->ptr->count = 1;
+}
+
+static void jvp_refcnt_inc(jv_complex* c) {
+  c->ptr->count++;
+}
+
+static int jvp_refcnt_dec(jv_complex* c) {
+  c->ptr->count--;
+  return c->ptr->count == 0;
+}
+
+static int jvp_refcnt_unshared(jv_complex* c) {
+  assert(c->ptr->count > 0);
+  return c->ptr->count == 1;
+}
+
+/*
+ * Simple values (true, false, null)
+ */
+
+jv_kind jv_get_kind(jv x) {
+  return x.kind;
+}
+
+static const jv JV_NULL = {JV_KIND_NULL, {0}};
+static const jv JV_FALSE = {JV_KIND_FALSE, {0}};
+static const jv JV_TRUE = {JV_KIND_TRUE, {0}};
+
+jv jv_true() {
+  return JV_TRUE;
+}
+
+jv jv_false() {
+  return JV_FALSE;
+}
+
+jv jv_null() {
+  return JV_NULL;
+}
+
+/*
+ * Numbers
+ */
+
+jv jv_number(double x) {
+  jv j;
+  j.kind = JV_KIND_NUMBER;
+  j.val.number = x;
+  return j;
+}
+
+double jv_number_value(jv j) {
+  assert(jv_get_kind(j) == JV_KIND_NUMBER);
+  return j.val.number;
+}
+
+
+/*
+ * Arrays (internal helpers)
+ */
+
+#define ARRAY_SIZE_ROUND_UP(n) (((n)*3)/2)
+
+static int imax(int a, int b) {
+  if (a>b) return a;
+  else return b;
+}
+
+//FIXME signed vs unsigned
+typedef struct {
+  jv_refcnt refcnt;
+  int length, alloc_length;
+  jv elements[];
+} jvp_array;
+
+static jvp_array* jvp_array_ptr(jv_complex* a) {
+  return (jvp_array*)a->ptr;
+}
+
+static jvp_array* jvp_array_alloc(unsigned size) {
+  jvp_array* a = malloc(sizeof(jvp_array) + sizeof(jv) * size);
+  a->refcnt.count = 1;
+  a->length = 0;
+  a->alloc_length = size;
+  return a;
+}
+
+static jv_complex jvp_array_new(unsigned size) {
+  jv_complex r = {&jvp_array_alloc(size)->refcnt, {0, 0}};
+  return r;
+}
+
+static void jvp_array_free(jv_complex* a) {
+  if (jvp_refcnt_dec(a)) {
+    jvp_array* array = jvp_array_ptr(a);
+    for (int i=0; i<array->length; i++) {
+      jv_free(array->elements[i]);
+    }
+    free(array);
+  }
+}
+
+static int jvp_array_length(jv_complex* a) {
+  return a->i[1] - a->i[0];
+}
+
+static jv* jvp_array_read(jv_complex* a, int i) {
+  assert(i >= 0 && i < jvp_array_length(a));
+  jvp_array* array = jvp_array_ptr(a);
+  assert(i + a->i[0] < array->length);
+  return &array->elements[i + a->i[0]];
+}
+
+static jv* jvp_array_write(jv_complex* a, int i) {
+  assert(i >= 0);
+  jvp_array* array = jvp_array_ptr(a);
+
+  int pos = i + a->i[0];
+  if (pos < array->alloc_length) {
+    // maybe we can update it in-place
+    // FIXME: this "optimisation" can cause circular references
+    #if 0
+    int can_write_past_end = 
+      array->length <= pos && /* the end of this array has never been used */
+      a->i[1] == array->length; /* the current slice sees the end of the array */
+    #endif
+    int can_write_past_end = 0;
+    if (can_write_past_end || jvp_refcnt_unshared(a)) {
+      // extend the array
+      for (int j = array->length; j <= pos; j++) {
+        array->elements[j] = JV_NULL;
+      }
+      array->length = imax(pos + 1, array->length);
+      a->i[1] = imax(pos + 1, array->length);
+      return &array->elements[pos];
+    }
+  }
+  
+  
+  int new_length = imax(i + 1, jvp_array_length(a));
+  jvp_array* new_array = jvp_array_alloc(ARRAY_SIZE_ROUND_UP(new_length));
+  int j;
+  for (j = 0; j < jvp_array_length(a); j++) {
+    new_array->elements[j] = jv_copy(array->elements[j + a->i[0]]);
+  }
+  for (; j < new_length; j++) {
+    new_array->elements[j] = JV_NULL;
+  }
+  new_array->length = new_length;
+  jvp_array_free(a);
+  a->ptr = &new_array->refcnt;
+  a->i[0] = 0;
+  a->i[1] = new_length;
+  return &new_array->elements[i];
+}
+
+static int jvp_array_equal(jv_complex* a, jv_complex* b) {
+  if (jvp_array_length(a) != jvp_array_length(b)) 
+    return 0;
+  if (jvp_array_ptr(a) == jvp_array_ptr(b) &&
+      a->i[0] == b->i[0]) 
+    return 1;
+  for (int i=0; i<jvp_array_length(a); i++) {
+    if (!jv_equal(jv_copy(*jvp_array_read(a, i)), 
+                  jv_copy(*jvp_array_read(b,i))))
+      return 0;
+  }
+  return 1;
+}
+
+static jv_complex jvp_array_slice(jv_complex* a, int start, int end) {
+  // FIXME: maybe slice should reallocate if the slice is small enough
+  assert(start <= end);
+  jvp_array* array = jvp_array_ptr(a);
+  assert(a->i[1] + end < array->length);
+  jv_complex slice = *a;
+  slice.i[0] += start;
+  slice.i[1] = slice.i[0] + (end - start);
+  return slice;
+}
+
+/*
+ * Arrays (public interface)
+ */
+
+jv jv_array_sized(int n) {
+  jv j;
+  j.kind = JV_KIND_ARRAY;
+  j.val.complex = jvp_array_new(n);
+  return j;
+}
+
+jv jv_array() {
+  return jv_array_sized(16);
+}
+
+int jv_array_length(jv j) {
+  assert(jv_get_kind(j) == JV_KIND_ARRAY);
+  int len = jvp_array_length(&j.val.complex);
+  jv_free(j);
+  return len;
+}
+
+jv jv_array_get(jv j, int idx) {
+  assert(jv_get_kind(j) == JV_KIND_ARRAY);
+  jv val = jv_copy(*jvp_array_read(&j.val.complex, idx));
+  jv_free(j);
+  return val;
+}
+
+jv jv_array_set(jv j, int idx, jv val) {
+  assert(jv_get_kind(j) == JV_KIND_ARRAY);
+  // copy/free of val,j coalesced
+  *jvp_array_write(&j.val.complex, idx) = val;
+  return j;
+}
+
+jv jv_array_append(jv j, jv val) {
+  // copy/free of val,j coalesced
+  return jv_array_set(j, jv_array_length(jv_copy(j)), val);
+}
+
+jv jv_array_concat(jv a, jv b) {
+  assert(jv_get_kind(a) == JV_KIND_ARRAY);
+  assert(jv_get_kind(b) == JV_KIND_ARRAY);
+
+  // FIXME: could be much faster
+  for (int i=0; i<jv_array_length(b); i++) {
+    a = jv_array_append(a, jv_array_get(jv_copy(b), i));
+  }
+  jv_free(b);
+  return a;
+}
+
+jv jv_array_slice(jv a, int start, int end) {
+  assert(jv_get_kind(a) == JV_KIND_ARRAY);
+  // copy/free of a coalesced
+  a.val.complex = jvp_array_slice(&a.val.complex, start, end);
+  return a;
+}
+
+
+/*
+ * Strings (internal helpers)
+ */
+
+typedef struct {
+  jv_refcnt refcnt;
+  uint32_t hash;
+  // high 31 bits are length, low bit is a flag 
+  // indicating whether hash has been computed.
+  uint32_t length_hashed;
+  char data[];
+} jvp_string;
+
+static jvp_string* jvp_string_ptr(jv_complex* a) {
+  return (jvp_string*)a->ptr;
+}
+
+static jvp_string* jvp_string_alloc(uint32_t size) {
+  jvp_string* s = malloc(sizeof(jvp_string) + size + 1);
+  s->refcnt.count = 1;
+  s->length_hashed = size << 1;
+  return s;
+}
+
+static jv_complex jvp_string_new(char* data, uint32_t length) {
+  jvp_string* s = jvp_string_alloc(length);
+  memcpy(s->data, data, length);
+  s->data[length] = 0;
+  jv_complex r = {&s->refcnt, {0,0}};
+  return r;
+}
+
+static void jvp_string_free(jv_complex* s) {
+  if (jvp_refcnt_dec(s)) {
+    jvp_string* str = jvp_string_ptr(s);
+    free(str);
+  }
+}
+
+static void jvp_string_free_p(jvp_string* s) {
+  jv_complex p = {&s->refcnt,{0,0}};
+  jvp_string_free(&p);
+}
+
+static jvp_string* jvp_string_copy_p(jvp_string* s) {
+  jv_complex p = {&s->refcnt,{0,0}};
+  jvp_refcnt_inc(&p);
+  return s;
+}
+
+static uint32_t jvp_string_length(jvp_string* s) {
+  return s->length_hashed >> 1;
+}
+
+static const uint32_t HASH_SEED = 0x432A9843;
+
+static uint32_t rotl32 (uint32_t x, int8_t r){
+  return (x << r) | (x >> (32 - r));
+}
+
+static uint32_t jvp_string_hash(jvp_string* str) {
+  if (str->length_hashed & 1) 
+    return str->hash;
+
+  /* The following is based on MurmurHash3.
+     MurmurHash3 was written by Austin Appleby, and is placed
+     in the public domain. */
+
+  const uint8_t* data = (const uint8_t*)str->data;
+  int len = (int)jvp_string_length(str);
+  const int nblocks = len / 4;
+
+  uint32_t h1 = HASH_SEED;
+
+  const uint32_t c1 = 0xcc9e2d51;
+  const uint32_t c2 = 0x1b873593;
+  const uint32_t* blocks = (const uint32_t *)(data + nblocks*4);
+
+  for(int i = -nblocks; i; i++) {
+    uint32_t k1 = blocks[i]; //FIXME: endianness/alignment
+    
+    k1 *= c1;
+    k1 = rotl32(k1,15);
+    k1 *= c2;
+    
+    h1 ^= k1;
+    h1 = rotl32(h1,13); 
+    h1 = h1*5+0xe6546b64;
+  }
+
+  const uint8_t* tail = (const uint8_t*)(data + nblocks*4);
+
+  uint32_t k1 = 0;
+
+  switch(len & 3) {
+  case 3: k1 ^= tail[2] << 16;
+  case 2: k1 ^= tail[1] << 8;
+  case 1: k1 ^= tail[0];
+          k1 *= c1; k1 = rotl32(k1,15); k1 *= c2; h1 ^= k1;
+  }
+
+  h1 ^= len;
+
+  h1 ^= h1 >> 16;
+  h1 *= 0x85ebca6b;
+  h1 ^= h1 >> 13;
+  h1 *= 0xc2b2ae35;
+  h1 ^= h1 >> 16;
+
+  str->length_hashed |= 1;
+  str->hash = h1;
+
+  return h1;
+}
+
+static int jvp_string_equal_hashed(jvp_string* a, jvp_string* b) {
+  assert(a->length_hashed & 1);
+  assert(b->length_hashed & 1);
+  if (a == b) return 1;
+  if (a->hash != b->hash) return 0;
+  if (a->length_hashed != b->length_hashed) return 0;
+  return memcmp(a->data, b->data, jvp_string_length(a)) == 0;
+}
+
+static int jvp_string_equal(jv_complex* a, jv_complex* b) {
+  jvp_string* stra = jvp_string_ptr(a);
+  jvp_string* strb = jvp_string_ptr(b);
+  if (jvp_string_length(stra) != jvp_string_length(strb)) return 0;
+  return memcmp(stra->data, strb->data, jvp_string_length(stra)) == 0;
+}
+
+/*
+ * Strings (public API)
+ */
+
+jv jv_string_sized(char* str, int len) {
+  jv j;
+  j.kind = JV_KIND_STRING;
+  j.val.complex = jvp_string_new(str, len);
+  return j;
+}
+
+jv jv_string(char* str) {
+  return jv_string_sized(str, strlen(str));
+}
+
+int jv_string_length(jv j) {
+  assert(jv_get_kind(j) == JV_KIND_STRING);
+  int r = jvp_string_length(jvp_string_ptr(&j.val.complex));
+  jv_free(j);
+  return r;
+}
+
+uint32_t jv_string_hash(jv j) {
+  assert(jv_get_kind(j) == JV_KIND_STRING);
+  uint32_t hash = jvp_string_hash(jvp_string_ptr(&j.val.complex));
+  jv_free(j);
+  return hash;
+}
+
+const char* jv_string_value(jv j) {
+  assert(jv_get_kind(j) == JV_KIND_STRING);
+  return jvp_string_ptr(&j.val.complex)->data;
+}
+
+/*
+ * Objects (internal helpers)
+ */
+
+struct object_slot {
+  int next;
+  jvp_string* string;
+  uint32_t hash;
+  jv value;
+};
+
+typedef struct {
+  jv_refcnt refcnt;
+  int first_free;
+  struct object_slot elements[];
+} jvp_object;
+
+
+/* warning: complex justification of alignment */
+static jv_complex jvp_object_new(int size) {
+  // Allocates an object of (size) slots and (size*2) hash buckets.
+
+  // size must be a power of two
+  assert(size > 0 && (size & (size - 1)) == 0);
+  jvp_object* obj = malloc(sizeof(jvp_object) + 
+                           sizeof(struct object_slot) * size +
+                           sizeof(int) * (size * 2));
+  obj->refcnt.count = 1;
+  for (int i=0; i<size; i++) {
+    obj->elements[i].next = i - 1;
+    obj->elements[i].string = 0;
+    obj->elements[i].hash = 0;
+    obj->elements[i].value = JV_NULL;
+  }
+  obj->first_free = size - 1;
+  int* hashbuckets = (int*)(&obj->elements[size]);
+  jv_complex r = {&obj->refcnt, 
+                  {size*2 - 1, (char*)hashbuckets - (char*)obj}};
+  for (int i=0; i<size*2; i++) {
+    hashbuckets[i] = -1;
+  }
+  return r;
+}
+
+static jvp_object* jvp_object_ptr(jv_complex* o) {
+  return (jvp_object*)o->ptr;
+}
+
+static uint32_t jvp_object_mask(jv_complex* o) {
+  return o->i[0];
+}
+
+static int jvp_object_size(jv_complex* o) {
+  return (o->i[0] + 1) >> 1;
+}
+
+static int* jvp_object_buckets(jv_complex* o) {
+  int* buckets = (int*)((char*)o->ptr + o->i[1]);
+  assert(buckets == (int*)&jvp_object_ptr(o)->elements[jvp_object_size(o)]);
+  return buckets;
+}
+
+static int* jvp_object_find_bucket(jv_complex* object, jvp_string* key) {
+  return jvp_object_buckets(object) + (jvp_object_mask(object) & jvp_string_hash(key));
+}
+
+static struct object_slot* jvp_object_get_slot(jv_complex* object, int slot) {
+  assert(slot == -1 || (slot >= 0 && slot < jvp_object_size(object)));
+  if (slot == -1) return 0;
+  else return &jvp_object_ptr(object)->elements[slot];
+}
+
+static struct object_slot* jvp_object_next_slot(jv_complex* object, struct object_slot* slot) {
+  return jvp_object_get_slot(object, slot->next);
+}
+
+static struct object_slot* jvp_object_find_slot(jv_complex* object, jvp_string* keystr, int* bucket) {
+  for (struct object_slot* curr = jvp_object_get_slot(object, *bucket); 
+       curr; 
+       curr = jvp_object_next_slot(object, curr)) {
+    if (jvp_string_equal_hashed(keystr, curr->string)) {
+      return curr;
+    }
+  }
+  return 0;
+}
+
+static struct object_slot* jvp_object_add_slot(jv_complex* object, jvp_string* key, int* bucket) {
+  jvp_object* o = jvp_object_ptr(object);
+  int newslot_idx = o->first_free;
+  struct object_slot* newslot = jvp_object_get_slot(object, newslot_idx);
+  if (newslot == 0) return 0;
+  o->first_free = newslot->next;
+  newslot->next = *bucket;
+  *bucket = newslot_idx;
+  newslot->hash = jvp_string_hash(key);
+  newslot->string = key;
+  return newslot;
+}
+
+static void jvp_object_free_slot(jv_complex* object, struct object_slot* slot) {
+  jvp_object* o = jvp_object_ptr(object);
+  slot->next = o->first_free;
+  assert(slot->string);
+  jvp_string_free_p(slot->string);
+  slot->string = 0;
+  jv_free(slot->value);
+  o->first_free = slot - jvp_object_get_slot(object, 0);
+}
+
+static jv* jvp_object_read(jv_complex* object, jvp_string* key) {
+  int* bucket = jvp_object_find_bucket(object, key);
+  struct object_slot* slot = jvp_object_find_slot(object, key, bucket);
+  if (slot == 0) return 0;
+  else return &slot->value;
+}
+
+static void jvp_object_free(jv_complex* o) {
+  if (jvp_refcnt_dec(o)) {
+    for (int i=0; i<jvp_object_size(o); i++) {
+      struct object_slot* slot = jvp_object_get_slot(o, i);
+      if (slot->string) {
+        jvp_string_free_p(slot->string);
+        jv_free(slot->value);
+      }
+    }
+    free(jvp_object_ptr(o));
+  }
+}
+
+static void jvp_object_rehash(jv_complex* object) {
+  assert(jvp_refcnt_unshared(object));
+  int size = jvp_object_size(object);
+  jv_complex new_object = jvp_object_new(size * 2);
+  for (int i=0; i<size; i++) {
+    struct object_slot* slot = jvp_object_get_slot(object, i);
+    if (!slot->string) continue;
+    
+    int* new_bucket = jvp_object_find_bucket(&new_object, slot->string);
+    assert(!jvp_object_find_slot(&new_object, slot->string, new_bucket));
+    struct object_slot* new_slot = jvp_object_add_slot(&new_object, slot->string, new_bucket);
+    assert(new_slot);
+    new_slot->value = slot->value;
+  }
+  // references are transported, just drop the old table
+  free(jvp_object_ptr(object));
+  *object = new_object;
+}
+
+static void jvp_object_unshare(jv_complex* object) {
+  if (jvp_refcnt_unshared(object))
+    return;
+
+  jv_complex new_object = jvp_object_new(jvp_object_size(object));
+  jvp_object_ptr(&new_object)->first_free = jvp_object_ptr(object)->first_free;
+  for (int i=0; i<jvp_object_size(&new_object); i++) {
+    struct object_slot* old_slot = jvp_object_get_slot(object, i);
+    struct object_slot* new_slot = jvp_object_get_slot(&new_object, i);
+    *new_slot = *old_slot;
+    if (old_slot->string) {
+      new_slot->string = jvp_string_copy_p(old_slot->string);
+      new_slot->value = jv_copy(old_slot->value);
+    }
+  }
+
+  int* old_buckets = jvp_object_buckets(object);
+  int* new_buckets = jvp_object_buckets(&new_object);
+  memcpy(new_buckets, old_buckets, sizeof(int) * jvp_object_size(&new_object)*2);
+
+  jvp_object_free(object);
+  *object = new_object;
+  assert(jvp_refcnt_unshared(object));
+}
+
+static jv* jvp_object_write(jv_complex* object, jvp_string* key) {
+  jvp_object_unshare(object);
+  int* bucket = jvp_object_find_bucket(object, key);
+  struct object_slot* slot = jvp_object_find_slot(object, key, bucket);
+  if (slot) {
+    // already has the key
+    jvp_string_free_p(key);
+  } else {
+    slot = jvp_object_add_slot(object, key, bucket);
+  }
+  if (slot == 0) {
+    jvp_object_rehash(object);
+    bucket = jvp_object_find_bucket(object, key);
+    assert(!jvp_object_find_slot(object, key, bucket));
+    slot = jvp_object_add_slot(object, key, bucket);
+    assert(slot);
+  }
+  return &slot->value;
+}
+
+static int jvp_object_delete(jv_complex* object, jvp_string* key) {
+  jvp_object_unshare(object);
+  int* bucket = jvp_object_find_bucket(object, key);
+  int* prev_ptr = bucket;
+  for (struct object_slot* curr = jvp_object_get_slot(object, *bucket); 
+       curr; 
+       curr = jvp_object_next_slot(object, curr)) {
+    if (jvp_string_equal_hashed(key, curr->string)) {
+      *prev_ptr = curr->next;
+      jvp_object_free_slot(object, curr);
+      return 1;
+    }
+    prev_ptr = &curr->next;
+  }
+  return 0;
+}
+
+/*
+ * Objects (public interface)
+ */
+#define DEFAULT_OBJECT_SIZE 8
+jv jv_object() {
+  jv j;
+  j.kind = JV_KIND_OBJECT;
+  j.val.complex = jvp_object_new(8);
+  return j;
+}
+
+jv jv_object_get(jv object, jv key) {
+  assert(jv_get_kind(object) == JV_KIND_OBJECT);
+  assert(jv_get_kind(key) == JV_KIND_STRING);
+  jv val = jv_copy(*jvp_object_read(&object.val.complex, jvp_string_ptr(&key.val.complex)));
+  jv_free(object);
+  jv_free(key);
+  return val;
+}
+
+jv jv_object_set(jv object, jv key, jv value) {
+  assert(jv_get_kind(object) == JV_KIND_OBJECT);
+  assert(jv_get_kind(key) == JV_KIND_STRING);
+  // copy/free of object, key, value coalesced
+  *jvp_object_write(&object.val.complex, jvp_string_ptr(&key.val.complex)) = value;
+  return object;
+}
+
+jv jv_object_delete(jv object, jv key) {
+  assert(jv_get_kind(object) == JV_KIND_OBJECT);
+  assert(jv_get_kind(key) == JV_KIND_STRING);
+  jvp_object_delete(&object.val.complex, jvp_string_ptr(&key.val.complex));
+  jv_free(key);
+  return object;
+}
+
+/*
+ * Object iteration (internal helpers)
+ */
+
+enum { ITER_FINISHED = -2 };
+
+int jv_object_iter_valid(jv object, int i) {
+  return i != ITER_FINISHED;
+}
+
+int jv_object_iter(jv object) {
+  assert(jv_get_kind(object) == JV_KIND_OBJECT);
+  return jv_object_iter_next(object, -1);
+}
+
+int jv_object_iter_next(jv object, int iter) {
+  assert(jv_get_kind(object) == JV_KIND_OBJECT);
+  assert(iter != ITER_FINISHED);
+  jv_complex* o = &object.val.complex;
+  struct object_slot* slot;
+  do {
+    iter++;
+    if (iter >= jvp_object_size(o)) 
+      return ITER_FINISHED;
+    slot = jvp_object_get_slot(o, iter);
+  } while (!slot->string);
+  return iter;
+}
+
+jv jv_object_iter_key(jv object, int iter) {
+  jvp_string* s = jvp_object_get_slot(&object.val.complex, iter)->string;
+  assert(s);
+  jv j;
+  j.kind = JV_KIND_STRING;
+  j.val.complex.ptr = &s->refcnt;
+  j.val.complex.i[0] = 0;
+  j.val.complex.i[1] = 0;
+  return jv_copy(j);
+}
+
+jv jv_object_iter_value(jv object, int iter) {
+  return jv_copy(jvp_object_get_slot(&object.val.complex, iter)->value);
+}
+
+/*
+ * Memory management
+ */
+jv jv_copy(jv j) {
+  if (jv_get_kind(j) == JV_KIND_ARRAY || 
+      jv_get_kind(j) == JV_KIND_STRING || 
+      jv_get_kind(j) == JV_KIND_OBJECT) {
+    jvp_refcnt_inc(&j.val.complex);
+  }
+  return j;
+}
+
+void jv_free(jv j) {
+  if (jv_get_kind(j) == JV_KIND_ARRAY) {
+    jvp_array_free(&j.val.complex);
+  } else if (jv_get_kind(j) == JV_KIND_STRING) {
+    jvp_string_free(&j.val.complex);
+  } else if (jv_get_kind(j) == JV_KIND_OBJECT) {
+    jvp_object_free(&j.val.complex);
+  }
+}
+
+/*
+ * Higher-level operations
+ */
+
+int jv_equal(jv a, jv b) {
+  int r;
+  if (jv_get_kind(a) != jv_get_kind(b)) {
+    r = 0;
+  } else {
+    switch (jv_get_kind(a)) {
+    case JV_KIND_NUMBER:
+      r = jv_number_value(a) == jv_number_value(b);
+      break;
+    case JV_KIND_ARRAY: {
+      r = jvp_array_equal(&a.val.complex, &b.val.complex);
+      break;
+    }
+    case JV_KIND_STRING: {
+      r = jvp_string_equal(&a.val.complex, &b.val.complex);
+      break;
+    }    
+    default:
+      r = 1;
+      break;
+    }
+  }
+  jv_free(a);
+  jv_free(b);
+  return r;
+}

c/jv.h

@@ -2,6 +2,8 @@
 #define JV_H
 
 #include <jansson.h>
+#include <stdint.h>
+#include <assert.h>
 
 static json_t* jv_lookup(json_t* t, json_t* k) {
   json_t* v;
@@ -38,4 +40,102 @@ static json_t* jv_insert(json_t* root, json_t* value, json_t** path, int pathlen
 }
 
 
+
+
+typedef enum {
+  JV_KIND_NULL,
+  JV_KIND_FALSE,
+  JV_KIND_TRUE,
+  JV_KIND_NUMBER,
+  JV_KIND_STRING,
+  JV_KIND_OBJECT,
+  JV_KIND_ARRAY
+} jv_kind;
+
+typedef struct {
+  size_t count;
+} jv_refcnt;
+
+typedef struct{
+  jv_refcnt* ptr;
+  int i[2];
+} jv_complex;
+
+typedef struct {
+  jv_kind kind;
+  union {
+    double number;
+    jv_complex complex;
+  } val;
+} jv;
+
+/*
+ * All jv_* functions consume (decref) input and produce (incref) output
+ * Except jv_copy
+ */
+
+jv_kind jv_get_kind(jv);
+
+jv jv_copy(jv);
+void jv_free(jv);
+
+int jv_equal(jv, jv);
+
+jv jv_null();
+jv jv_true();
+jv jv_false();
+
+jv jv_number(double);
+double jv_number_value(jv);
+
+jv jv_array();
+jv jv_array_sized(int);
+int jv_array_length(jv);
+jv jv_array_get(jv, int);
+jv jv_array_set(jv, int, jv);
+jv jv_array_append(jv, jv);
+jv jv_array_concat(jv, jv);
+jv jv_array_slice(jv, int, int);
+
+
+jv jv_string(char*);
+jv jv_string_sized(char*, int);
+int jv_string_length(jv);
+uint32_t jv_string_hash(jv);
+const char* jv_string_value(jv);
+
+jv jv_object();
+jv jv_object_get(jv object, jv key);
+jv jv_object_set(jv object, jv key, jv value);
+jv jv_object_delete(jv object, jv key);
+
+int jv_object_iter(jv);
+int jv_object_iter_next(jv, int);
+int jv_object_iter_valid(jv, int);
+jv jv_object_iter_key(jv, int);
+jv jv_object_iter_value(jv, int);
+
+
 #endif
+
+
+/*
+
+true/false/null:
+check kind
+
+number:
+introduce/eliminate jv
+to integer
+
+array:
+copy
+free
+slice
+index
+update
+
+updateslice?
+
+
+ */

c/jv_print.c

@@ -0,0 +1,45 @@
+#include "jv.h"
+#include <stdio.h>
+
+void jv_dump(jv x) {
+  switch (jv_get_kind(x)) {
+  case JV_KIND_NULL:
+    printf("null");
+    break;
+  case JV_KIND_FALSE:
+    printf("false");
+    break;
+  case JV_KIND_TRUE:
+    printf("true");
+    break;
+  case JV_KIND_NUMBER:
+    printf("%f", jv_number_value(x));
+    break;
+  case JV_KIND_STRING:
+    // FIXME: all sorts of broken
+    printf("\"%s\"", jv_string_value(x));
+    break;
+  case JV_KIND_ARRAY: {
+    printf("[");
+    for (int i=0; i<jv_array_length(jv_copy(x)); i++) {
+      if (i!=0) printf(", ");
+      jv_dump(jv_array_get(jv_copy(x), i));
+    }
+    printf("]");
+    break;
+  }
+  case JV_KIND_OBJECT: {
+    printf("{");
+    int first = 1;
+    for (int i = jv_object_iter(x); jv_object_iter_valid(x,i); i = jv_object_iter_next(x,i)) {
+      if (!first) printf(", ");
+      first = 0;
+      jv_dump(jv_object_iter_key(x, i));
+      printf(": ");
+      jv_dump(jv_object_iter_value(x, i));
+    }
+    printf("}");
+  }
+  }
+  jv_free(x);
+}

c/jvtest.c

@@ -0,0 +1,135 @@
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+#include "jv.h"
+
+void jv_dump(jv);
+
+int main(){
+  /// Arrays and numbers
+  {
+    jv a = jv_array();
+    assert(jv_get_kind(a) == JV_KIND_ARRAY);
+    assert(jv_array_length(jv_copy(a)) == 0);
+    assert(jv_array_length(jv_copy(a)) == 0);
+  
+    a = jv_array_append(a, jv_number(42));
+    assert(jv_array_length(jv_copy(a)) == 1);
+    assert(jv_number_value(jv_array_get(jv_copy(a), 0)) == 42);
+
+    jv a2 = jv_array_append(jv_array(), jv_number(42));
+    assert(jv_equal(jv_copy(a), jv_copy(a)));
+    assert(jv_equal(jv_copy(a2), jv_copy(a2)));
+    assert(jv_equal(jv_copy(a), jv_copy(a2)));
+    assert(jv_equal(jv_copy(a2), jv_copy(a)));
+    jv_free(a2);
+
+    a2 = jv_array_append(jv_array(), jv_number(19));
+    assert(!jv_equal(jv_copy(a), jv_copy(a2)));
+    assert(!jv_equal(jv_copy(a2), jv_copy(a)));
+    jv_free(a2);
+
+
+    assert(a.val.complex.ptr->count == 1);
+    a = jv_array_append(a, jv_copy(a));
+    assert(a.val.complex.ptr->count == 1);
+
+    assert(jv_array_length(jv_copy(a)) == 2);
+    assert(jv_number_value(jv_array_get(jv_copy(a), 0)) == 42);
+
+    for (int i=0; i<10; i++) {
+      jv subarray = jv_array_get(jv_copy(a), 1);
+      assert(jv_get_kind(subarray) == JV_KIND_ARRAY);
+      assert(jv_array_length(jv_copy(subarray)) == 1);
+      assert(jv_number_value(jv_array_get(jv_copy(subarray), 0)) == 42);
+      jv_free(subarray);
+    }
+
+
+    jv subarray = jv_array_get(jv_copy(a), 1);
+    assert(jv_get_kind(subarray) == JV_KIND_ARRAY);
+    assert(jv_array_length(jv_copy(subarray)) == 1);
+    assert(jv_number_value(jv_array_get(jv_copy(subarray), 0)) == 42);
+
+    jv sub2 = jv_copy(subarray);
+    sub2 = jv_array_append(sub2, jv_number(19));
+
+    assert(jv_get_kind(sub2) == JV_KIND_ARRAY);
+    assert(jv_array_length(jv_copy(sub2)) == 2);
+    assert(jv_number_value(jv_array_get(jv_copy(sub2), 0)) == 42);
+    assert(jv_number_value(jv_array_get(jv_copy(sub2), 1)) == 19);
+
+    assert(jv_get_kind(subarray) == JV_KIND_ARRAY);
+    assert(jv_array_length(jv_copy(subarray)) == 1);
+    assert(jv_number_value(jv_array_get(jv_copy(subarray), 0)) == 42);
+
+    jv_free(subarray);
+
+    void* before = sub2.val.complex.ptr;
+    sub2 = jv_array_append(sub2, jv_number(200));
+    void* after = sub2.val.complex.ptr;
+    assert(before == after);
+    jv_free(sub2);
+
+    jv a3 = jv_array_append(jv_copy(a), jv_number(19));
+    assert(jv_array_length(jv_copy(a3)) == 3);
+    assert(jv_number_value(jv_array_get(jv_copy(a3), 0)) == 42);
+    assert(jv_array_length(jv_array_get(jv_copy(a3), 1)) == 1);
+    assert(jv_number_value(jv_array_get(jv_copy(a3), 2)) == 19);
+    jv_free(a3);
+
+
+    assert(jv_array_length(jv_copy(a)) == 2);
+    assert(jv_number_value(jv_array_get(jv_copy(a), 0)) == 42);
+    assert(jv_array_length(jv_array_get(jv_copy(a), 1)) == 1);
+
+
+    jv_dump(jv_copy(a)); printf("\n");
+    jv_free(a);
+  }
+
+
+  /// Strings
+  {
+    assert(jv_equal(jv_string("foo"), jv_string_sized("foo", 3)));
+    char nasty[] = "foo\0";
+    jv shortstr = jv_string(nasty), longstr = jv_string_sized(nasty, sizeof(nasty));
+    assert(jv_string_length(shortstr) == strlen(nasty));
+    assert(jv_string_length(longstr) == sizeof(nasty));
+
+  
+    char a1s[] = "hello", a2s[] = "hello", bs[] = "goodbye";
+    jv a1 = jv_string(a1s), a2 = jv_string(a2s), b = jv_string(bs);
+    assert(jv_equal(jv_copy(a1), jv_copy(a2)));
+    assert(jv_equal(jv_copy(a2), jv_copy(a1)));
+    assert(!jv_equal(jv_copy(a1), jv_copy(b)));
+    
+    assert(jv_string_hash(jv_copy(a1)) == jv_string_hash(jv_copy(a1)));
+    assert(jv_string_hash(jv_copy(a1)) == jv_string_hash(jv_copy(a2)));
+    assert(jv_string_hash(jv_copy(b)) != jv_string_hash(jv_copy(a1)));
+    jv_free(a1);
+    jv_free(a2);
+    jv_free(b);
+  }
+
+  /// Objects
+  {
+    jv o1 = jv_object();
+    o1 = jv_object_set(o1, jv_string("foo"), jv_number(42));
+    o1 = jv_object_set(o1, jv_string("bar"), jv_number(24));
+    assert(jv_number_value(jv_object_get(jv_copy(o1), jv_string("foo"))) == 42);
+    assert(jv_number_value(jv_object_get(jv_copy(o1), jv_string("bar"))) == 24);
+
+    jv o2 = jv_object_set(jv_copy(o1), jv_string("foo"), jv_number(420));
+    o2 = jv_object_set(o2, jv_string("bar"), jv_number(240));
+    assert(jv_number_value(jv_object_get(jv_copy(o1), jv_string("foo"))) == 42);
+    assert(jv_number_value(jv_object_get(jv_copy(o1), jv_string("bar"))) == 24);
+    assert(jv_number_value(jv_object_get(jv_copy(o2), jv_string("foo"))) == 420);
+    jv_free(o1);
+    assert(jv_number_value(jv_object_get(jv_copy(o2), jv_string("bar"))) == 240);
+
+    jv_dump(jv_copy(o2)); printf("\n");
+
+    jv_free(o2);
+  }
+}