From 3403b0c7256435560b63f828da92026c5d4c898b Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 26 Apr 2023 13:36:34 -0300
Subject: New module 'lpcset'

For code related to compact sets.
---
 lpcset.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 lpcset.c

(limited to 'lpcset.c')

diff --git a/lpcset.c b/lpcset.c
new file mode 100644
index 0000000..9ecf475
--- /dev/null
+++ b/lpcset.c
@@ -0,0 +1,69 @@
+
+#include "lptypes.h"
+#include "lpcset.h"
+
+
+/*
+** Add to 'c' the index of the (only) bit set in byte 'b'
+*/
+static int onlybit (int c, int b) {
+  if ((b & 0xF0) != 0) { c += 4; b >>= 4; }
+  if ((b & 0x0C) != 0) { c += 2; b >>= 2; }
+  if ((b & 0x02) != 0) { c += 1; }
+  return c;
+}
+
+
+/*
+** Check whether a charset is empty (returns IFail), singleton (IChar),
+** full (IAny), or none of those (ISet). When singleton, 'info.aux1'
+** returns which character it is. When generic set, 'info' returns
+** information about its range.
+*/
+Opcode charsettype (const byte *cs, charsetinfo *info) {
+  int low0, low1, high0, high1;
+  for (low1 = 0; low1 < CHARSETSIZE && cs[low1] == 0; low1++)
+    /* find lowest byte with a 1-bit */;
+  if (low1 == CHARSETSIZE)
+    return IFail;  /* no characters in set */
+  for (high1 = CHARSETSIZE - 1; cs[high1] == 0; high1--)
+    /* find highest byte with a 1-bit; low1 is a sentinel */;
+  if (low1 == high1) {  /* only one byte with 1-bits? */
+    int b = cs[low1];
+    if ((b & (b - 1)) == 0) {  /* does byte has only one 1-bit? */
+      info->aux1 = onlybit(low1 * BITSPERCHAR, b);  /* get that bit */
+      return IChar;  /* single character */
+    }
+  }
+  for (low0 = 0; low0 < CHARSETSIZE && cs[low0] == 0xFF; low0++)
+    /* find lowest byte with a 0-bit */;
+  if (low0 == CHARSETSIZE)
+    return IAny;  /* set has all bits set */
+  for (high0 = CHARSETSIZE - 1; cs[high0] == 0xFF; high0--)
+    /* find highest byte with a 0-bit; low0 is a sentinel */;
+  if (high1 - low1 <= high0 - low0) {  /* range of 1s smaller than of 0s? */
+    info->aux1 = low1;
+    info->size = high1 - low1 + 1;
+    info->deflt = 0;  /* all discharged bits were 0 */
+  }
+  else {
+    info->aux1 = low0;
+    info->size = high0 - low0 + 1;
+    info->deflt = 0xFF;  /* all discharged bits were 1 */
+  }
+  return ISet;
+}
+
+
+/*
+** Get a byte from a compact charset. If index is inside the charset
+** range, get the byte from the supporting charset (correcting it
+** by the offset). Otherwise, return the default for the set.
+*/
+byte getbytefromcharset (const byte *cs, const charsetinfo *info,
+                                int index) {
+  if (index < info->size)
+    return cs[info->aux1 + index];
+  else return info->deflt;
+}
+
-- 
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