feat: Implements Atoms.

compile_flags.txt

@@ -0,0 +1,2 @@
+-std=c99
+-Iinclude

include/atom.h

@@ -0,0 +1,9 @@
+#ifndef ATOM_INDCLUDED
+#define ATOM_INDCLUDED
+
+extern       int   Atom_length(const char *str);
+extern const char *Atom_new   (const char *str, int len);
+extern const char *Atom_string(const char *str);
+extern const char *Atom_int   (long n);
+
+#endif

src/atom.c

@@ -0,0 +1,156 @@
+// Includes
+#include "atom.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include "assert.h"
+
+// TODO: Include "mem.h" when that's available.
+
+// Macros
+# define NELEMS(x) ((sizeof (x))/(sizeof ((x)[0])))
+
+// Data
+static struct atom {
+  struct atom *link;
+  int len;
+  char *str;
+} *buckets[2048];
+
+// scatter is used for hashing byte sequences, each number was randomly generated.
+static unsigned long scatter[] = {
+2078917053, 143302914, 1027100827, 1953210302, 755253631, 2002600785,
+1405390230, 45248011, 1099951567, 433832350, 2018585307, 438263339,
+813528929, 1703199216, 618906479, 573714703, 766270699, 275680090,
+1510320440, 1583583926, 1723401032, 1965443329, 1098183682, 1636505764,
+980071615, 1011597961, 643279273, 1315461275, 157584038, 1069844923,
+471560540, 89017443, 1213147837, 1498661368, 2042227746, 1968401469,
+1353778505, 1300134328, 2013649480, 306246424, 1733966678, 1884751139,
+744509763, 400011959, 1440466707, 1363416242, 973726663, 59253759,
+1639096332, 336563455, 1642837685, 1215013716, 154523136, 593537720,
+704035832, 1134594751, 1605135681, 1347315106, 302572379, 1762719719,
+269676381, 774132919, 1851737163, 1482824219, 125310639, 1746481261,
+1303742040, 1479089144, 899131941, 1169907872, 1785335569, 485614972,
+907175364, 382361684, 885626931, 200158423, 1745777927, 1859353594,
+259412182, 1237390611, 48433401, 1902249868, 304920680, 202956538,
+348303940, 1008956512, 1337551289, 1953439621, 208787970, 1640123668,
+1568675693, 478464352, 266772940, 1272929208, 1961288571, 392083579,
+871926821, 1117546963, 1871172724, 1771058762, 139971187, 1509024645,
+109190086, 1047146551, 1891386329, 994817018, 1247304975, 1489680608,
+706686964, 1506717157, 579587572, 755120366, 1261483377, 884508252,
+958076904, 1609787317, 1893464764, 148144545, 1415743291, 2102252735,
+1788268214, 836935336, 433233439, 2055041154, 2109864544, 247038362,
+299641085, 834307717, 1364585325, 23330161, 457882831, 1504556512,
+1532354806, 567072918, 404219416, 1276257488, 1561889936, 1651524391,
+618454448, 121093252, 1010757900, 1198042020, 876213618, 124757630,
+2082550272, 1834290522, 1734544947, 1828531389, 1982435068, 1002804590,
+1783300476, 1623219634, 1839739926, 69050267, 1530777140, 1802120822,
+316088629, 1830418225, 488944891, 1680673954, 1853748387, 946827723,
+1037746818, 1238619545, 1513900641, 1441966234, 367393385, 928306929,
+946006977, 985847834, 1049400181, 1956764878, 36406206, 1925613800,
+2081522508, 2118956479, 1612420674, 1668583807, 1800004220, 1447372094,
+523904750, 1435821048, 923108080, 216161028, 1504871315, 306401572,
+2018281851, 1820959944, 2136819798, 359743094, 1354150250, 1843084537,
+1306570817, 244413420, 934220434, 672987810, 1686379655, 1301613820,
+1601294739, 484902984, 139978006, 503211273, 294184214, 176384212,
+281341425, 228223074, 147857043, 1893762099, 1896806882, 1947861263,
+1193650546, 273227984, 1236198663, 2116758626, 489389012, 593586330,
+275676551, 360187215, 267062626, 265012701, 719930310, 1621212876,
+2108097238, 2026501127, 1865626297, 894834024, 552005290, 1404522304,
+48964196, 5816381, 1889425288, 188942202, 509027654, 36125855,
+365326415, 790369079, 264348929, 513183458, 536647531, 13672163,
+313561074, 1730298077, 286900147, 1549759737, 1699573055, 776289160,
+2143346068, 1975249606, 1136476375, 262925046, 92778659, 1856406685,
+1884137923, 53392249, 1735424165, 1602280572
+};
+
+// Functions
+
+const char *Atom_string(const char *str) {
+  assert(str);
+  return Atom_new(str, strlen(str));
+}
+
+const char *Atom_int(long n) {
+  char str[43];
+  char *s = str + sizeof str;
+  unsigned long m;
+  
+  // Both limits are in 2's compliment.
+  // LONG_MIN's magnitude is one more than LONG_MAX because the range is asymetric.
+  // `m` just contains the magnitude. We must do this becuse there's no way to negate
+  // n and keep its full magnitude.
+  if (n == LONG_MIN)
+    m = LONG_MAX + 1UL;
+  else if (n < 0)
+    // If n is not min, we can safely negate it to get the magnitude.
+    m = -n;
+  else
+    m = n;
+  
+  // The pointer starts at one past the buffer.
+  // We pre-decrement on each write, and use a
+  // `do` to easily account for 0.
+  do
+    *--s = m%10 + '0';
+  while ((m /= 10) > 0);
+  if (n < 0)
+    *--s = '-';
+
+  return Atom_new(s, (str + sizeof str) - s);
+}
+
+const char *Atom_new(const char *str, int len) {
+  unsigned long h;
+  int i;
+  struct atom *p;
+
+  assert(str);
+  assert(len >= 0);
+
+  // Hash the string.
+  for (h = 0, i = 0; i < len; i++)
+    h = (h<<1) + scatter[(unsigned char)str[i]];
+  h %= NELEMS(buckets);
+
+  for (p = buckets[h]; p; p = p -> link)
+    if (len == p->len) {
+      for (i = 0; i < len && p->str[i] == str[i]; )
+        i++;
+      if (i == len)
+        return p->str;
+    }
+  // Allocate a new entry.
+  // Struct size, plus the string lenght, plus null terminator.
+  // TODO: Replace malloc with ALLOC from "mem.h" when that's implemented.
+  p = malloc(sizeof (*p) + len + 1);
+  p->len = len;
+  p->str = (char *)(p + 1);
+  if (len > 0)
+    memcpy(p->str, str, len);
+  p->str[len] = '\0';
+  
+  // This works only if buckets are initialized to null pointers.
+  // Which in this case is true because buckets has a static lifetime.
+  p->link = buckets[h];
+  buckets[h] = p;
+
+  return p->str;
+}
+
+int Atom_length(const char *str) {
+  struct atom *p;
+  int i;
+
+  assert(str);
+  // TODO: Could hash to find the bucket instead.
+  for (i = 0; i < NELEMS(buckets); i++)
+    for (p = buckets[i]; p; p = p->link)
+      if (p->str == str)
+        return p->len;
+  
+  // Should not call Atom_length witn a non-atom string.
+  assert(0);
+  return 0;
+}