path: root/src/cairo-truetype-subset.c

/* cairo - a vector graphics library with display and print output
 *
 * Copyright © 2004 Red Hat, Inc
 *
 * This library is free software; you can redistribute it and/or
 * modify it either under the terms of the GNU Lesser General Public
 * License version 2.1 as published by the Free Software Foundation
 * (the "LGPL") or, at your option, under the terms of the Mozilla
 * Public License Version 1.1 (the "MPL"). If you do not alter this
 * notice, a recipient may use your version of this file under either
 * the MPL or the LGPL.
 *
 * You should have received a copy of the LGPL along with this library
 * in the file COPYING-LGPL-2.1; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 * You should have received a copy of the MPL along with this library
 * in the file COPYING-MPL-1.1
 *
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.1 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
 * OF ANY KIND, either express or implied. See the LGPL or the MPL for
 * the specific language governing rights and limitations.
 *
 * The Original Code is the cairo graphics library.
 *
 * The Initial Developer of the Original Code is Red Hat, Inc.
 *
 * Contributor(s):
 *	Kristian Høgsberg <krh@redhat.com>
 *	Adrian Johnson <ajohnson@redneon.com>
 */

#include <string.h>
#include "cairoint.h"
#include "cairo-scaled-font-subsets-private.h"
#include "cairo-truetype-subset-private.h"


typedef struct subset_glyph subset_glyph_t;
struct subset_glyph {
    int parent_index;
    unsigned long location;
};

typedef struct _cairo_truetype_font {

    cairo_scaled_font_subset_t *scaled_font_subset;

    struct {
	char *base_font;
	unsigned int num_glyphs;
	int *widths;
	long x_min, y_min, x_max, y_max;
	long ascent, descent;
    } base;

    subset_glyph_t *glyphs;
    const cairo_scaled_font_backend_t *backend;
    int num_glyphs_in_face;
    int checksum_index;
    cairo_array_t output;
    cairo_array_t string_offsets;
    unsigned long last_offset;
    unsigned long last_boundary;
    int *parent_to_subset;
    cairo_status_t status;

} cairo_truetype_font_t;

static int
cairo_truetype_font_use_glyph (cairo_truetype_font_t *font, int glyph);

#define ARRAY_LENGTH(a) ( (sizeof (a)) / (sizeof ((a)[0])) )

#define SFNT_VERSION			0x00010000
#define SFNT_STRING_MAX_LENGTH  65535

#ifdef WORDS_BIGENDIAN

#define cpu_to_be16(v) (v)
#define be16_to_cpu(v) (v)
#define cpu_to_be32(v) (v)
#define be32_to_cpu(v) (v)

#else

static inline uint16_t
cpu_to_be16(uint16_t v)
{
    return (v << 8) | (v >> 8);
}

static inline uint16_t
be16_to_cpu(uint16_t v)
{
    return cpu_to_be16 (v);
}

static inline uint32_t
cpu_to_be32(uint32_t v)
{
    return (cpu_to_be16 (v) << 16) | cpu_to_be16 (v >> 16);
}

static inline uint32_t
be32_to_cpu(uint32_t v)
{
    return cpu_to_be32 (v);
}

#endif

static cairo_status_t
_cairo_truetype_font_create (cairo_scaled_font_subset_t  *scaled_font_subset,
			     cairo_truetype_font_t      **font_return)
{
    cairo_status_t status = CAIRO_STATUS_NO_MEMORY;
    cairo_truetype_font_t *font;
    const cairo_scaled_font_backend_t *backend;
    tt_head_t head;
    tt_hhea_t hhea;
    tt_maxp_t maxp;
    tt_name_t *name;
    tt_name_record_t *record;
    unsigned long size;
    int i, j;

    backend = scaled_font_subset->scaled_font->backend;
    if (!backend->load_truetype_table)
	return CAIRO_INT_STATUS_UNSUPPORTED;

    /* FIXME: We should either support subsetting vertical fonts, or fail on
     * vertical.  Currently font_options_t doesn't have vertical flag, but
     * it should be added in the future.  For now, the freetype backend
     * returns UNSUPPORTED in load_truetype_table if the font is vertical.
     *
     *  if (cairo_font_options_get_vertical_layout (scaled_font_subset->scaled_font))
     *   return CAIRO_INT_STATUS_UNSUPPORTED;
     */

    size = sizeof (tt_head_t);
    if (backend->load_truetype_table (scaled_font_subset->scaled_font,
                                      TT_TAG_head, 0, (unsigned char *) &head,
                                      &size) != CAIRO_STATUS_SUCCESS)
	return CAIRO_INT_STATUS_UNSUPPORTED;

    size = sizeof (tt_maxp_t);
    if (backend->load_truetype_table (scaled_font_subset->scaled_font,
                                      TT_TAG_maxp, 0, (unsigned char *) &maxp,
                                      &size) != CAIRO_STATUS_SUCCESS)
	return CAIRO_INT_STATUS_UNSUPPORTED;

    size = sizeof (tt_hhea_t);
    if (backend->load_truetype_table (scaled_font_subset->scaled_font,
                                      TT_TAG_hhea, 0, (unsigned char *) &hhea,
                                      &size) != CAIRO_STATUS_SUCCESS)
	return CAIRO_INT_STATUS_UNSUPPORTED;

    size = 0;
    if (backend->load_truetype_table (scaled_font_subset->scaled_font,
                                      TT_TAG_name, 0, NULL,
                                      &size) != CAIRO_STATUS_SUCCESS)
	return CAIRO_INT_STATUS_UNSUPPORTED;
    name = malloc(size);
    if (name == NULL)
        return CAIRO_STATUS_NO_MEMORY;
    backend->load_truetype_table (scaled_font_subset->scaled_font,
                                 TT_TAG_name, 0, (unsigned char *) name,
                                 &size);

    font = malloc (sizeof (cairo_truetype_font_t));
    if (font == NULL)
	goto fail0;

    font->backend = backend;
    font->num_glyphs_in_face = be16_to_cpu (maxp.num_glyphs);
    font->scaled_font_subset = scaled_font_subset;

    font->last_offset = 0;
    font->last_boundary = 0;
    _cairo_array_init (&font->output, sizeof (char));
    if (_cairo_array_grow_by (&font->output, 4096) != CAIRO_STATUS_SUCCESS)
	goto fail1;
    font->glyphs = calloc (font->num_glyphs_in_face + 1, sizeof (subset_glyph_t));
    if (font->glyphs == NULL)
	goto fail2;

    font->parent_to_subset = calloc (font->num_glyphs_in_face, sizeof (int));
    if (font->parent_to_subset == NULL)
	goto fail3;

    font->base.num_glyphs = 0;
    font->base.x_min = (int16_t) be16_to_cpu (head.x_min);
    font->base.y_min = (int16_t) be16_to_cpu (head.y_min);
    font->base.x_max = (int16_t) be16_to_cpu (head.x_max);
    font->base.y_max = (int16_t) be16_to_cpu (head.y_max);
    font->base.ascent = (int16_t) be16_to_cpu (hhea.ascender);
    font->base.descent = (int16_t) be16_to_cpu (hhea.descender);

    /* Extract the font name from the name table. At present this
     * just looks for the Mac platform/Roman encoded font name. It
     * should be extended to use any suitable font name in the
     * name table. If the mac/roman font name is not found a
     * CairoFont-x-y name is created.
     */
    font->base.base_font = NULL;
    for (i = 0; i < be16_to_cpu(name->num_records); i++) {
        record = &(name->records[i]);
        if ((be16_to_cpu (record->platform) == 1) &&
            (be16_to_cpu (record->encoding) == 0) &&
            (be16_to_cpu (record->name) == 4)) { 
            font->base.base_font = malloc (be16_to_cpu(record->length) + 1);
            if (font->base.base_font) {
                strncpy(font->base.base_font,
                        ((char*)name) + be16_to_cpu (name->strings_offset) + be16_to_cpu (record->offset),
                        be16_to_cpu (record->length));
                font->base.base_font[be16_to_cpu (record->length)] = 0;
            }
            break;
        }
    }

    free (name);
    name = NULL;

    if (font->base.base_font == NULL) {
        font->base.base_font = malloc (30);
        if (font->base.base_font == NULL)
            goto fail4; 
        snprintf(font->base.base_font, 30, "CairoFont-%u-%u",
                 scaled_font_subset->font_id,
                 scaled_font_subset->subset_id);
    }

    for (i = 0, j = 0; font->base.base_font[j]; j++) {
	if (font->base.base_font[j] == ' ')
	    continue;
	font->base.base_font[i++] = font->base.base_font[j];
    }
    font->base.base_font[i] = '\0';

    font->base.widths = calloc (font->num_glyphs_in_face, sizeof (int));
    if (font->base.widths == NULL)
	goto fail5;

    _cairo_array_init (&font->string_offsets, sizeof (unsigned long));
    if (_cairo_array_grow_by (&font->string_offsets, 10) != CAIRO_STATUS_SUCCESS)
	goto fail6;

    font->status = CAIRO_STATUS_SUCCESS;

    *font_return = font;

    return CAIRO_STATUS_SUCCESS;

 fail6:
    free (font->base.widths);
 fail5:
    free (font->base.base_font);
 fail4:
    free (font->parent_to_subset);
 fail3:
    free (font->glyphs);
 fail2:
    _cairo_array_fini (&font->output);
 fail1:
    free (font);
 fail0:
    if (name)
	free (name);
    return status;
}

static void
cairo_truetype_font_destroy (cairo_truetype_font_t *font)
{
    _cairo_array_fini (&font->string_offsets);
    free (font->base.widths);
    free (font->base.base_font);
    free (font->parent_to_subset);
    free (font->glyphs);
    _cairo_array_fini (&font->output);
    free (font);
}

static cairo_status_t
cairo_truetype_font_allocate_write_buffer (cairo_truetype_font_t  *font,
					   size_t		   length,
					   unsigned char	 **buffer)
{
    cairo_status_t status;

    status = _cairo_array_allocate (&font->output, length, (void **) buffer);
    if (status)
	return status;

    return CAIRO_STATUS_SUCCESS;
}

static cairo_status_t
cairo_truetype_font_write (cairo_truetype_font_t *font,
			   const void            *data,
			   size_t                 length)
{
    cairo_status_t status;

    status = _cairo_array_append_multiple (&font->output, data, length);
    if (status)
	return status;

    return CAIRO_STATUS_SUCCESS;
}

static void
cairo_truetype_font_write_be16 (cairo_truetype_font_t *font,
				uint16_t               value)
{
    uint16_t be16_value;

    be16_value = cpu_to_be16 (value);
    cairo_truetype_font_write (font, &be16_value, sizeof be16_value);
}

static void
cairo_truetype_font_write_be32 (cairo_truetype_font_t *font,
				uint32_t               value)
{
    uint32_t be32_value;

    be32_value = cpu_to_be32 (value);
    cairo_truetype_font_write (font, &be32_value, sizeof be32_value);
}

static unsigned long
cairo_truetype_font_align_output (cairo_truetype_font_t *font)
{
    int length, aligned, pad;
    unsigned char *padding;

    length = _cairo_array_num_elements (&font->output);
    aligned = (length + 3) & ~3;
    pad = aligned - length;

    if (pad) {
	cairo_truetype_font_allocate_write_buffer (font, pad, &padding);
	memset (padding, 0, pad);
    }

    return aligned;
}

static void
cairo_truetype_font_check_boundary (cairo_truetype_font_t *font,
				    unsigned long          boundary)
{
    if (boundary - font->last_offset > SFNT_STRING_MAX_LENGTH)
    {
        _cairo_array_append(&font->string_offsets, &font->last_boundary);
        font->last_offset = font->last_boundary;
    }
    font->last_boundary = boundary;
}

static int
cairo_truetype_font_write_cmap_table (cairo_truetype_font_t *font,
				      unsigned long          tag)
{
    unsigned int i;

    cairo_truetype_font_write_be16 (font, 0);
    cairo_truetype_font_write_be16 (font, 1);

    cairo_truetype_font_write_be16 (font, 1);
    cairo_truetype_font_write_be16 (font, 0);
    cairo_truetype_font_write_be32 (font, 12);

    /* Output a format 6 encoding table. */

    cairo_truetype_font_write_be16 (font, 6);
    cairo_truetype_font_write_be16 (font, 10 + 2 * (font->base.num_glyphs - 1));
    cairo_truetype_font_write_be16 (font, 0);
    cairo_truetype_font_write_be16 (font, 1); /* First glyph */
    cairo_truetype_font_write_be16 (font, font->base.num_glyphs - 1);
    for (i = 1; i < font->base.num_glyphs; i++)
	cairo_truetype_font_write_be16 (font, i);

    return font->status;
}

static int
cairo_truetype_font_write_generic_table (cairo_truetype_font_t *font,
					 unsigned long          tag)
{
    cairo_status_t status;
    unsigned char *buffer;
    unsigned long size;

    size = 0;
    if (font->backend->load_truetype_table( font->scaled_font_subset->scaled_font,
					    tag, 0, NULL, &size) != CAIRO_STATUS_SUCCESS) {
        font->status = CAIRO_INT_STATUS_UNSUPPORTED;
        return font->status;
    }
    status = cairo_truetype_font_allocate_write_buffer (font, size, &buffer);
    /* XXX: Need to check status here. */
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        tag, 0, buffer, &size);
    return 0;
}

static void
cairo_truetype_font_remap_composite_glyph (cairo_truetype_font_t *font,
					   unsigned char         *buffer)
{
    tt_glyph_data_t *glyph_data;
    tt_composite_glyph_t *composite_glyph;
    int num_args;
    int has_more_components;
    unsigned short flags;
    unsigned short index;

    glyph_data = (tt_glyph_data_t *) buffer;
    if ((int16_t)be16_to_cpu (glyph_data->num_contours) >= 0)
        return;

    composite_glyph = &glyph_data->glyph;
    do {
        flags = be16_to_cpu (composite_glyph->flags);
        has_more_components = flags & TT_MORE_COMPONENTS;
        index = cairo_truetype_font_use_glyph (font, be16_to_cpu (composite_glyph->index));
        composite_glyph->index = cpu_to_be16 (index);
        num_args = 1;
        if (flags & TT_ARG_1_AND_2_ARE_WORDS)
            num_args += 1;
        if (flags & TT_WE_HAVE_A_SCALE)
            num_args += 1;
        else if (flags & TT_WE_HAVE_AN_X_AND_Y_SCALE)
            num_args += 2;
        else if (flags & TT_WE_HAVE_A_TWO_BY_TWO)
            num_args += 3;
        composite_glyph = (tt_composite_glyph_t *) &(composite_glyph->args[num_args]);
    } while (has_more_components);
}

static int
cairo_truetype_font_write_glyf_table (cairo_truetype_font_t *font,
				      unsigned long          tag)
{
    cairo_status_t status;
    unsigned long start_offset, index, size, next;
    tt_head_t header;
    unsigned long begin, end;
    unsigned char *buffer;
    unsigned int i;
    union {
	unsigned char *bytes;
	uint16_t      *short_offsets;
	uint32_t      *long_offsets;
    } u;

    size = sizeof (tt_head_t);
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        TT_TAG_head, 0, (unsigned char*) &header, &size);
    
    if (be16_to_cpu (header.index_to_loc_format) == 0)
	size = sizeof (int16_t) * (font->num_glyphs_in_face + 1);
    else
	size = sizeof (int32_t) * (font->num_glyphs_in_face + 1);

    u.bytes = malloc (size);
    if (u.bytes == NULL) {
	font->status = CAIRO_STATUS_NO_MEMORY;
	return font->status;
    }
    if (font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                            TT_TAG_loca, 0, u.bytes, &size) != CAIRO_STATUS_SUCCESS) {
        font->status = CAIRO_INT_STATUS_UNSUPPORTED;
        return font->status;
    }

    start_offset = _cairo_array_num_elements (&font->output);
    for (i = 0; i < font->base.num_glyphs; i++) {
	index = font->glyphs[i].parent_index;
	if (be16_to_cpu (header.index_to_loc_format) == 0) {
	    begin = be16_to_cpu (u.short_offsets[index]) * 2;
	    end = be16_to_cpu (u.short_offsets[index + 1]) * 2;
	}
	else {
	    begin = be32_to_cpu (u.long_offsets[index]);
	    end = be32_to_cpu (u.long_offsets[index + 1]);
	}

	size = end - begin;

        next = cairo_truetype_font_align_output (font);
        cairo_truetype_font_check_boundary (font, next);
        font->glyphs[i].location = next - start_offset;

	status = cairo_truetype_font_allocate_write_buffer (font, size, &buffer);
	if (status)
	    break;
        if (size != 0) {
            font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                                TT_TAG_glyf, begin, buffer, &size);
            cairo_truetype_font_remap_composite_glyph (font, buffer);
        }
    }

    font->glyphs[i].location =
	cairo_truetype_font_align_output (font) - start_offset;

    free (u.bytes);

    return font->status;
}

static int
cairo_truetype_font_write_head_table (cairo_truetype_font_t *font,
                                      unsigned long          tag)
{
    unsigned char *buffer;
    unsigned long size;

    size = 0;
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        tag, 0, NULL, &size);
    font->checksum_index = _cairo_array_num_elements (&font->output) + 8;
    font->status = cairo_truetype_font_allocate_write_buffer (font, size, &buffer);
    font->backend->load_truetype_table( font->scaled_font_subset->scaled_font,
                                        tag, 0, buffer, &size);
    return font->status;
}

static int cairo_truetype_font_write_hhea_table (cairo_truetype_font_t *font, unsigned long tag)
{
    tt_hhea_t *hhea;
    unsigned long size;

    size = sizeof (tt_hhea_t);
    font->status = cairo_truetype_font_allocate_write_buffer (font, size, (unsigned char **) &hhea);
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        tag, 0, (unsigned char *) hhea, &size);
    hhea->num_hmetrics = cpu_to_be16 ((uint16_t)(font->base.num_glyphs));
    return font->status;
}

static int
cairo_truetype_font_write_hmtx_table (cairo_truetype_font_t *font,
				      unsigned long          tag)
{
    cairo_status_t status;
    unsigned long size;
    unsigned long long_entry_size;
    unsigned long short_entry_size;
    short *p;
    unsigned int i;
    tt_hhea_t hhea;
    int num_hmetrics;

    size = sizeof (tt_hhea_t);
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        TT_TAG_hhea, 0, (unsigned char*) &hhea, &size);
    num_hmetrics = be16_to_cpu(hhea.num_hmetrics);

    for (i = 0; i < font->base.num_glyphs; i++) {
        long_entry_size = 2 * sizeof (int16_t);
        short_entry_size = sizeof (int16_t);
        status = cairo_truetype_font_allocate_write_buffer (font, long_entry_size,
							  (unsigned char **) &p);
        if (font->glyphs[i].parent_index < num_hmetrics) {
            if (font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                                    TT_TAG_hmtx,
                                                    font->glyphs[i].parent_index * long_entry_size,
                                                    (unsigned char *) p, &long_entry_size) != CAIRO_STATUS_SUCCESS) {
                font->status = CAIRO_INT_STATUS_UNSUPPORTED;
                return font->status;
            }
        }
        else
        {
            if (font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                                    TT_TAG_hmtx,
                                                    (num_hmetrics - 1) * long_entry_size,
                                                    (unsigned char *) p, &short_entry_size) != CAIRO_STATUS_SUCCESS) {
                font->status = CAIRO_INT_STATUS_UNSUPPORTED;
                return font->status;
            }
            font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                                TT_TAG_hmtx,
                                                num_hmetrics * long_entry_size +
                                                (font->glyphs[i].parent_index - num_hmetrics) * short_entry_size,
                                                (unsigned char *) (p + 1), &short_entry_size);
        }
        font->base.widths[i] = be16_to_cpu (p[0]);
    }

    return font->status;
}

static int
cairo_truetype_font_write_loca_table (cairo_truetype_font_t *font,
				      unsigned long          tag)
{
    unsigned int i;
    tt_head_t header;
    unsigned long size;

    size = sizeof(tt_head_t);
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        TT_TAG_head, 0, (unsigned char*) &header, &size);

    if (be16_to_cpu (header.index_to_loc_format) == 0)
    {
	for (i = 0; i < font->base.num_glyphs + 1; i++)
	    cairo_truetype_font_write_be16 (font, font->glyphs[i].location / 2);
    } else {
	for (i = 0; i < font->base.num_glyphs + 1; i++)
	    cairo_truetype_font_write_be32 (font, font->glyphs[i].location);
    }

    return font->status;
}

static int
cairo_truetype_font_write_maxp_table (cairo_truetype_font_t *font,
				      unsigned long          tag)
{
    tt_maxp_t *maxp;
    unsigned long size;

    size = sizeof (tt_maxp_t);
    font->status = cairo_truetype_font_allocate_write_buffer (font, size, (unsigned char **) &maxp);
    font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
                                        tag, 0, (unsigned char *) maxp, &size);
    maxp->num_glyphs = cpu_to_be16 (font->base.num_glyphs);
    return font->status;
}

typedef struct table table_t;
struct table {
    unsigned long tag;
    int (*write) (cairo_truetype_font_t *font, unsigned long tag);
};

static const table_t truetype_tables[] = {
    /* As we write out the glyf table we remap composite glyphs.
     * Remapping composite glyphs will reference the sub glyphs the
     * composite glyph is made up of.  That needs to be done first so
     * we have all the glyphs in the subset before going further. */
    { TT_TAG_glyf, cairo_truetype_font_write_glyf_table },
    { TT_TAG_cmap, cairo_truetype_font_write_cmap_table },
    { TT_TAG_cvt,  cairo_truetype_font_write_generic_table },
    { TT_TAG_fpgm, cairo_truetype_font_write_generic_table },
    { TT_TAG_head, cairo_truetype_font_write_head_table },
    { TT_TAG_hhea, cairo_truetype_font_write_hhea_table },
    { TT_TAG_hmtx, cairo_truetype_font_write_hmtx_table },
    { TT_TAG_loca, cairo_truetype_font_write_loca_table },
    { TT_TAG_maxp, cairo_truetype_font_write_maxp_table },
    { TT_TAG_name, cairo_truetype_font_write_generic_table },
    { TT_TAG_prep, cairo_truetype_font_write_generic_table },
};

static cairo_status_t
cairo_truetype_font_write_offset_table (cairo_truetype_font_t *font)
{
    cairo_status_t status;
    unsigned char *table_buffer;
    size_t table_buffer_length;
    unsigned short search_range, entry_selector, range_shift;
    int num_tables;

    num_tables = ARRAY_LENGTH (truetype_tables);
    search_range = 1;
    entry_selector = 0;
    while (search_range * 2 <= num_tables) {
	search_range *= 2;
	entry_selector++;
    }
    search_range *= 16;
    range_shift = num_tables * 16 - search_range;

    cairo_truetype_font_write_be32 (font, SFNT_VERSION);
    cairo_truetype_font_write_be16 (font, num_tables);
    cairo_truetype_font_write_be16 (font, search_range);
    cairo_truetype_font_write_be16 (font, entry_selector);
    cairo_truetype_font_write_be16 (font, range_shift);

    /* Allocate space for the table directory. Each directory entry
     * will be filled in by cairo_truetype_font_update_entry() after
     * the table is written. */
    table_buffer_length = ARRAY_LENGTH (truetype_tables) * 16;
    status = cairo_truetype_font_allocate_write_buffer (font, table_buffer_length,
						      &table_buffer);
    if (status)
	return status;

    return font->status;
}

static uint32_t
cairo_truetype_font_calculate_checksum (cairo_truetype_font_t *font,
					unsigned long          start,
					unsigned long          end)
{
    uint32_t *padded_end;
    uint32_t *p;
    uint32_t checksum;
    char *data;

    checksum = 0;
    data = _cairo_array_index (&font->output, 0);
    p = (uint32_t *) (data + start);
    padded_end = (uint32_t *) (data + ((end + 3) & ~3));
    while (p < padded_end)
	checksum += *p++;

    return checksum;
}

static void
cairo_truetype_font_update_entry (cairo_truetype_font_t *font,
				  int                    index,
				  unsigned long          tag,
				  unsigned long          start,
				  unsigned long          end)
{
    uint32_t *entry;

    entry = _cairo_array_index (&font->output, 12 + 16 * index);
    entry[0] = cpu_to_be32 ((uint32_t)tag);
    entry[1] = cpu_to_be32 (cairo_truetype_font_calculate_checksum (font, start, end));
    entry[2] = cpu_to_be32 ((uint32_t)start);
    entry[3] = cpu_to_be32 ((uint32_t)(end - start));
}

static cairo_status_t
cairo_truetype_font_generate (cairo_truetype_font_t  *font,
			      const char            **data,
			      unsigned long          *length,
			      const unsigned long   **string_offsets,
			      unsigned long          *num_strings)
{
    unsigned long start, end, next;
    uint32_t checksum, *checksum_location;
    unsigned int i;

    if (cairo_truetype_font_write_offset_table (font))
	goto fail;

    start = cairo_truetype_font_align_output (font);
    end = start;

    end = 0;
    for (i = 0; i < ARRAY_LENGTH (truetype_tables); i++) {
	if (truetype_tables[i].write (font, truetype_tables[i].tag))
	    goto fail;

	end = _cairo_array_num_elements (&font->output);
	next = cairo_truetype_font_align_output (font);
	cairo_truetype_font_update_entry (font, i, truetype_tables[i].tag,
					start, end);
        cairo_truetype_font_check_boundary (font, next);
	start = next;
    }

    checksum =
	0xb1b0afba - cairo_truetype_font_calculate_checksum (font, 0, end);
    checksum_location = _cairo_array_index (&font->output, font->checksum_index);
    *checksum_location = cpu_to_be32 (checksum);

    *data = _cairo_array_index (&font->output, 0);
    *length = _cairo_array_num_elements (&font->output);
    *num_strings = _cairo_array_num_elements (&font->string_offsets);
    if (*num_strings != 0)
	*string_offsets = _cairo_array_index (&font->string_offsets, 0);
    else
	*string_offsets = NULL;

 fail:
    return font->status;
}

static int
cairo_truetype_font_use_glyph (cairo_truetype_font_t *font, int glyph)
{
    if (font->parent_to_subset[glyph] == 0) {
	font->parent_to_subset[glyph] = font->base.num_glyphs;
	font->glyphs[font->base.num_glyphs].parent_index = glyph;
	font->base.num_glyphs++;
    }

    return font->parent_to_subset[glyph];
}

cairo_status_t
_cairo_truetype_subset_init (cairo_truetype_subset_t    *truetype_subset,
			     cairo_scaled_font_subset_t	*font_subset)
{
    cairo_truetype_font_t *font;
    cairo_status_t status;
    const char *data = NULL; /* squelch bogus compiler warning */
    unsigned long length = 0; /* squelch bogus compiler warning */
    unsigned long parent_glyph, offsets_length;
    unsigned int i;
    const unsigned long *string_offsets = NULL;
    unsigned long num_strings = 0;

    status = _cairo_truetype_font_create (font_subset, &font);
    if (status)
	return status;

    for (i = 0; i < font->scaled_font_subset->num_glyphs; i++) {
	parent_glyph = font->scaled_font_subset->glyphs[i];
	cairo_truetype_font_use_glyph (font, parent_glyph);
    }

    status = cairo_truetype_font_generate (font, &data, &length,
					 &string_offsets, &num_strings);
    if (status)
	goto fail1;

    truetype_subset->base_font = strdup (font->base.base_font);
    if (truetype_subset->base_font == NULL)
	goto fail1;

    truetype_subset->widths = calloc (sizeof (int), font->base.num_glyphs);
    if (truetype_subset->widths == NULL)
	goto fail2;
    for (i = 0; i < font->base.num_glyphs; i++)
	truetype_subset->widths[i] = font->base.widths[i];

    truetype_subset->x_min = font->base.x_min;
    truetype_subset->y_min = font->base.y_min;
    truetype_subset->x_max = font->base.x_max;
    truetype_subset->y_max = font->base.y_max;
    truetype_subset->ascent = font->base.ascent;
    truetype_subset->descent = font->base.descent;

    truetype_subset->data = malloc (length);
    if (truetype_subset->data == NULL)
	goto fail3;

    memcpy (truetype_subset->data, data, length);
    truetype_subset->data_length = length;

    offsets_length = num_strings * sizeof (unsigned long);
    truetype_subset->string_offsets = malloc (offsets_length);
    if (truetype_subset->string_offsets == NULL)
	goto fail4;

    memcpy (truetype_subset->string_offsets, string_offsets, offsets_length);
    truetype_subset->num_string_offsets = num_strings;

    cairo_truetype_font_destroy (font);

    return CAIRO_STATUS_SUCCESS;

 fail4:
    free (truetype_subset->data);
 fail3:
    free (truetype_subset->widths);
 fail2:
    free (truetype_subset->base_font);
 fail1:
    cairo_truetype_font_destroy (font);

    return status;
}

void
_cairo_truetype_subset_fini (cairo_truetype_subset_t *subset)
{
    free (subset->base_font);
    free (subset->widths);
    free (subset->data);
    free (subset->string_offsets);
}