From 4325ec3bbc1e06200d91bc79686051bd1b0b9ddb Mon Sep 17 00:00:00 2001
From: Mattias Andrée <maandree@kth.se>
Date: Sun, 17 Jul 2022 16:35:42 +0200
Subject: Fix two bugs and add documentation
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Signed-off-by: Mattias Andrée <maandree@kth.se>
---
 libparsepsf.c |  4 +--
 libparsepsf.h | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/libparsepsf.c b/libparsepsf.c
index 9649f63..485cce1 100644
--- a/libparsepsf.c
+++ b/libparsepsf.c
@@ -326,7 +326,7 @@ libparsepsf_parse_font(const void *data, size_t size, struct libparsepsf_font *f
 		if (header.psf2.height * ((header.psf2.width + 7) / 8) != header.psf2.charsize)
 			goto ebfont;
 		if (header.psf2.version > PSF2_MAXVERSION)
-			*unrecognised_versionp = 0;
+			*unrecognised_versionp = 1;
 		fontp->num_glyphs = (size_t)header.psf2.num_glyphs;
 		fontp->height     = (size_t)header.psf2.height;
 		fontp->width      = (size_t)header.psf2.width;
@@ -423,7 +423,7 @@ libparsepsf_get_glyph(const struct libparsepsf_font *font, const char *c, size_t
 		glyph = (size_t)cp;
 		if (glyph >= font->num_glyphs)
 			return 0;
-		glyph -= 1;
+		glyph += 1;
 		goto out;
 
 	} else if (remp) {
diff --git a/libparsepsf.h b/libparsepsf.h
index b1984b4..d13c062 100644
--- a/libparsepsf.h
+++ b/libparsepsf.h
@@ -6,22 +6,119 @@
 #include <stddef.h>
 
 
+/**
+ * Glyph trie
+ */
 struct libparsepsf_unimap {
+
+	/**
+	 * Mapping for next byte in a longer sequences
+	 */
 	struct libparsepsf_unimap *nonterminal[256];
-	size_t terminal[256]; /* index + 1, 0 if not used */
+
+	/**
+	 * Unless the byte index maps to 0, mapped to value
+	 * less 1 is the glyph index to use for the sequence
+	 * if there is no longer sequence
+	 */
+	size_t terminal[256];
 };
 
+/**
+ * Parsed PSF font structure
+ */
 struct libparsepsf_font {
+
+	/**
+	 * The number of glyphs in the font
+	 */
 	size_t num_glyphs;
+
+	/**
+	 * The bit-height of each glyph
+	 */
 	size_t height;
+
+	/**
+	 * The bit-width of each glyph
+	 */
 	size_t width;
+
+	/**
+	 * The glyph data
+	 * 
+	 * Each glyph is `.height * (.width / 8 + (.width % 8 ? 1 : 0))`
+	 * bytes large. Each glyph is right-padded to a multiple of 8 bits,
+	 * and are oriented in row-major and most-signficant-bit-first order,
+	 * meaning that the bit 0x80 in the first byte for a glyph represents
+	 * the left-most, top-most bit in the, and 0x40 in the same byte
+	 * represents the bit directly right to it. Bit on means ink on,
+	 * bit off means ink off.
+	 */
 	uint8_t *glyph_data;
+
+	/**
+	 * Glyph trie, maps from byte sequences to glyph indices;
+	 * you can use `libparsepsf_get_glyph` to search it
+	 * (enumeration has to be done manually); not that an
+	 * entry can be multiple characters wide, for example
+	 * to deal with context dependent glyphs and grapheme
+	 * clusters
+	 * 
+	 * `NULL` if unicode character points map directly
+	 * (identity mapping) to glyph indices; and UTF-8 the
+	 * assumed encoding
+	 */
 	struct libparsepsf_unimap *map;
 };
 
 
+/**
+ * Deallocate font
+ * 
+ * @param  font  Pointer to the data to deallocate
+ */
 void libparsepsf_destroy_font(struct libparsepsf_font *font);
+
+/**
+ * Parse a PSF font file
+ * 
+ * @param   data                   The font file content
+ * @param   size                   The number of bytes in `data`
+ * @param   fontp                  Output parameter for the font, should be deallocated
+ *                                 using `libparsepsf_destroy_font` when no longer
+ *                                 needed (only allocated on success completion)
+ * @param   unrecognised_versionp  Normally set to 0; set to 1 if the minor version in
+ *                                 the font file is unrecognised (backwards-compatibility
+ *                                 is assumed, so it will still be parsed as a supported
+ *                                 font file)
+ * @return                         0 on successful completion, -1 on failure
+ * @throws  ENOMEM                 Failed to allocate enough memory
+ * @throws  EBFONT                 Corrupt or unsupported font file
+ */
 int libparsepsf_parse_font(const void *data, size_t size, struct libparsepsf_font *fontp, uint32_t *unrecognised_versionp);
+
+/**
+ * Get the next glyph to print for a text
+ *
+ * @param   font     The parsed font, created with `libparsepsf_parse_font`
+ * @param   c        The current position in the text (the text shall be
+ *                   completely loaded to guarantee multi-characters glyphs
+ *                   are properly printed)
+ * @param   remp     The number of bytes in `c`, will be updated to reflect
+ *                   the value it shall have when the function is called
+ *                   again, with `*next_cp` as `c` (that is, the number of
+ *                   bytes in the found byte sequence is subtracted);
+ *                   if `NULL`, the text ends when a NUL byte is found
+ * @param   next_cp  Output parameter for the next position in the text;
+ *                   may be `NULL`
+ * @return           The index of the glyph, plus 1; 0 if the glyph if the
+ *                   end of the text is reached or if no glyph is found,
+ *                   or (only if `font->map` is `NULL`) if an illegal byte
+ *                   sequence was found
+ * @throws  EILSEQ   If an illegal byte sequence was found (only if
+ *                   `font->map` is `NULL`)
+ */
 size_t libparsepsf_get_glyph(const struct libparsepsf_font *font, const char *c, size_t *remp, const char **next_cp);
 
 #endif
-- 
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