[ruby/prism] Add cp51932 encoding file

ruby/prism@c67a0f4c78

Author: wildmaples

prism/enc/pm_cp51932.c

@@ -0,0 +1,57 @@
+#include "prism/enc/pm_encoding.h"
+
+static size_t
+pm_encoding_cp51932_char_width(const uint8_t *b, ptrdiff_t n) {
+    // These are the single byte characters.
+    if (*b < 0x80) {
+        return 1;
+    }
+
+    // These are the double byte characters.
+    if (
+        (n > 1) &&
+        ((b[0] >= 0xa1 && b[0] <= 0xfe) || (b[0] == 0x8e)) &&
+        (b[1] >= 0xa1 && b[1] <= 0xfe)
+    ) {
+        return 2;
+    }
+
+    return 0;
+}
+
+static size_t
+pm_encoding_cp51932_alpha_char(const uint8_t *b, ptrdiff_t n) {
+    if (pm_encoding_cp51932_char_width(b, n) == 1) {
+        return pm_encoding_ascii_alpha_char(b, n);
+    } else {
+        return 0;
+    }
+}
+
+static size_t
+pm_encoding_cp51932_alnum_char(const uint8_t *b, ptrdiff_t n) {
+    if (pm_encoding_cp51932_char_width(b, n) == 1) {
+        return pm_encoding_ascii_alnum_char(b, n);
+    } else {
+        return 0;
+    }
+}
+
+static bool
+pm_encoding_cp51932_isupper_char(const uint8_t *b, ptrdiff_t n) {
+    if (pm_encoding_cp51932_char_width(b, n) == 1) {
+        return pm_encoding_ascii_isupper_char(b, n);
+    } else {
+        return 0;
+    }
+}
+
+/** cp51932 encoding */
+pm_encoding_t pm_encoding_cp51932 = {
+    .name = "cp51932",
+    .char_width = pm_encoding_cp51932_char_width,
+    .alnum_char = pm_encoding_cp51932_alnum_char,
+    .alpha_char = pm_encoding_cp51932_alpha_char,
+    .isupper_char = pm_encoding_cp51932_isupper_char,
+    .multibyte = true
+};