Changeset 32704cb in mainline for kernel/generic/src/lib/string.c

Timestamp:

2009-03-31T18:50:09Z (15 years ago)

Author:

Jiri Svoboda <jirik.svoboda@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

b54d2f1

Parents:

0dd1d444

Message:

Slightly decompile character encoder.

File:

• kernel/generic/src/lib/string.c (modified) (2 diffs)

kernel/generic/src/lib/string.c

@@ -45 +45 @@
 char invalch = '?';
 
-/** Byte mask consisting of bits 0 - (@n - 1) */
+/** Byte mask consisting of lowest @n bits (out of eight). */
 #define LO_MASK_8(n) ((uint8_t)((1 << (n)) - 1))
+
+/** Byte mask consisting of lowest @n bits (out of 32). */
+#define LO_MASK_32(n) ((uint32_t)((1 << (n)) - 1))
+
+/** Byte mask consisting of highest @n bits (out of eight). */
+#define HI_MASK_8(n) (~LO_MASK_8(8 - (n)))
 
 /** Number of data bits in a UTF-8 continuation byte. */
@@ -145 +151 @@
 bool utf8_encode(const wchar_t ch, char *str, index_t *index, index_t limit)
 {
+        uint32_t cc;            /* Unsigned version of ch. */
+
+        int cbytes;             /* Number of continuation bytes. */
+        int b0_bits;            /* Number of data bits in first byte. */
+        int i;
+
         if (*index > limit)
                 return false;
-        
-        if ((ch >= 0) && (ch <= 127)) {
-                /* Plain ASCII (code points 0 .. 127) */
-                str[*index] = ch & 0x7f;
-                return true;
-        }
-        
-        if ((ch >= 128) && (ch <= 2047)) {
-                /* Code points 128 .. 2047 */
-                if (*index + 1 > limit)
-                        return false;
-                
-                str[*index] = 0xc0 | ((ch >> 6) & 0x1f);
-                (*index)++;
-                str[*index] = 0x80 | (ch & 0x3f);
-                return true;
-        }
-        
-        if ((ch >= 2048) && (ch <= 65535)) {
-                /* Code points 2048 .. 65535 */
-                if (*index + 2 > limit)
-                        return false;
-                
-                str[*index] = 0xe0 | ((ch >> 12) & 0x0f);
-                (*index)++;
-                str[*index] = 0x80 | ((ch >> 6) & 0x3f);
-                (*index)++;
-                str[*index] = 0x80 | (ch & 0x3f);
-                return true;
-        }
-        
-        if ((ch >= 65536) && (ch <= 1114111)) {
-                /* Code points 65536 .. 1114111 */
-                if (*index + 3 > limit)
-                        return false;
-                
-                str[*index] = 0xf0 | ((ch >> 18) & 0x07);
-                (*index)++;
-                str[*index] = 0x80 | ((ch >> 12) & 0x3f);
-                (*index)++;
-                str[*index] = 0x80 | ((ch >> 6) & 0x3f);
-                (*index)++;
-                str[*index] = 0x80 | (ch & 0x3f);
-                return true;
-        }
-        
-        return false;
+
+        if (ch < 0)
+                return false;
+
+        /* Bit operations should only be done on unsigned numbers. */
+        cc = (uint32_t) ch;
+
+        /* Determine how many continuation bytes are needed. */
+        if ((cc & ~LO_MASK_32(7)) == 0) {
+                b0_bits = 7;
+                cbytes = 0;
+        } else if ((cc & ~LO_MASK_32(11)) == 0) {
+                b0_bits = 5;
+                cbytes = 1;
+        } else if ((cc & ~LO_MASK_32(16)) == 0) {
+                b0_bits = 4;
+                cbytes = 2;
+        } else if ((cc & ~LO_MASK_32(21)) == 0) {
+                b0_bits = 3;
+                cbytes = 3;
+        } else {
+                /* Codes longer than 21 bits are not supported. */
+                return false;
+        }
+
+        /* Check for available space in buffer. */
+        if (*index + cbytes > limit)
+                return false;
+
+        /* Encode continuation bytes. */
+        for (i = cbytes; i > 0; --i) {
+                str[*index + i] = 0x80 | (cc & LO_MASK_32(CONT_BITS));
+                cc = cc >> CONT_BITS;
+        }
+
+        /* Encode first byte. */
+        str[*index] = (cc & LO_MASK_32(b0_bits)) | HI_MASK_8(8 - b0_bits - 1);
+
+        /* Advance index. */
+        *index += cbytes;
+        
+        return true;
 }