From 6318ddb69ad8380694bbca35ca5a72230c2ee694 Mon Sep 17 00:00:00 2001
From: Nicholas Noll <nbnoll@eml.cc>
Date: Thu, 28 Oct 2021 11:55:47 -0700
Subject: Feat(libunicode): cleaned up decode/encode

Additionally, decode can now apply backwards on a byte string.
---
 sys/libunicode/decodeprev.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 sys/libunicode/decodeprev.c

(limited to 'sys/libunicode/decodeprev.c')

diff --git a/sys/libunicode/decodeprev.c b/sys/libunicode/decodeprev.c
new file mode 100644
index 0000000..27dced6
--- /dev/null
+++ b/sys/libunicode/decodeprev.c
@@ -0,0 +1,60 @@
+#include "internal.h"
+
+#define ACCEPT 0
+#define REJECT 12
+
+static uint8 decode[] = {
+    /*
+     * the first part of the table maps bytes to character classes that
+     * to reduce the size of the transition table and create bitmasks.
+     */
+         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+         1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,  9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
+         7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+         8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
+        10,3,3,3,3,3,3,3,3,3,3,3,3,4,3,3, 11,6,6,6,5,8,8,8,8,8,8,8,8,8,8,8,
+    /*
+     * The second part is a transition table that maps a combination
+     * of a state of the automaton and a character class to a state.
+     */
+    //   0  1  2  3  4  5  6  7  8  9 10 11
+         0,24,12,12,12,12,12,24,12,24,12,12,
+         0,24,12,12,12,12,12,24,12,24,12,12,
+        12,36, 0,12,12,12,12,48,12,36,12,12,
+        12,60,12, 0, 0,12,12,72,12,72,12,12,
+        12,60,12, 0,12,12,12,72,12,72, 0,12,
+        12,12,12,12,12, 0, 0,12,12,12,12,12,
+        12,12,12,12,12,12,12,12,12,12,12, 0
+};
+
+int
+utf8·decodeprev(byte *s, rune *r)
+{
+    int   n;
+    rune  v;
+    uint8 b, t, d, x=ACCEPT;
+
+    v=0, n=0, d=0;
+nextbyte:
+    b = ((uint8 *)s)[-n++];
+    t = decode[b];
+    x = decode[256+x+t];
+
+    if(x > REJECT && n < UTFmax){
+        v = v | ((b & TMask) << d);
+        d += 6;
+        goto nextbyte;
+    }
+
+    if(x != ACCEPT)
+        *r = RuneErr;
+    else{
+        v |= (((0xFFu >> t) & b) << d);
+        *r = v;
+    }
+
+    return n;
+}
-- 
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