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#include "wp_compact_text.h"
#include <string.h>

static uint16_t wp_compact_le16(const uint8_t *p)
{
    return (uint16_t)((uint16_t)p[0] | ((uint16_t)p[1] << 8));
}

void wp_compact_stats_clear(WpCompactStats *stats)
{
    if (stats != NULL) {
        memset(stats, 0, sizeof(*stats));
    }
}

static bool wp_compact_write_token(uint16_t *out,
                                   size_t out_capacity,
                                   size_t *count,
                                   uint16_t value,
                                   WpCompactStats *stats)
{
    if (count == NULL) {
        return false;
    }
    if (*count >= out_capacity || out == NULL) {
        if (stats != NULL) {
            stats->output_truncated = true;
        }
        return false;
    }
    out[(*count)++] = value;
    if (stats != NULL) {
        stats->tokens_written++;
    }
    return true;
}

bool wp_compact_decode_token_stream(const uint8_t *src,
                                    size_t src_len,
                                    uint16_t *out,
                                    size_t out_capacity,
                                    size_t *out_count,
                                    WpCompactStats *stats)
{
    size_t pos = 0;
    size_t count = 0;
    bool ok = true;

    if (out_count != NULL) {
        *out_count = 0;
    }
    wp_compact_stats_clear(stats);

    if (src == NULL || out_count == NULL || (out_capacity > 0U && out == NULL)) {
        if (stats != NULL) {
            stats->input_truncated = true;
        }
        return false;
    }

    while (pos < src_len) {
        uint8_t b = src[pos];
        uint16_t token;

        if (b == 0U) {
            pos++;
            if (stats != NULL) {
                stats->hit_terminator = true;
            }
            /* The original stores a trailing zero word after stopping.  Keep
             * that sentinel outside the caller-visible token count. */
            if (out != NULL && count < out_capacity) {
                out[count] = 0;
            } else if (out_capacity == 0U || out == NULL) {
                if (stats != NULL) {
                    stats->output_truncated = true;
                }
                ok = false;
            }
            break;
        }

        if (b == 0xC0U) {
            if (pos + 3U >= src_len) {
                pos = src_len;
                if (stats != NULL) {
                    stats->input_truncated = true;
                }
                ok = false;
                break;
            }
            token = wp_compact_le16(src + pos + 1U);
            pos += 4U;
            if (stats != NULL) {
                stats->c0_word_tokens++;
            }
        } else {
            pos++;
            if (b == 0xFFU) {
                token = 0x007EU;
                if (stats != NULL) {
                    stats->ff_tilde_escapes++;
                }
            } else if (b == 0x7EU) {
                token = 0xFC3AU;
                if (stats != NULL) {
                    stats->tilde_markers++;
                }
            } else {
                token = b;
            }
        }

        if (!wp_compact_write_token(out, out_capacity, &count, token, stats)) {
            ok = false;
            break;
        }
    }

    if (pos >= src_len && (stats == NULL || !stats->hit_terminator) && ok) {
        if (stats != NULL) {
            stats->input_truncated = true;
        }
        ok = false;
    }

    if (stats != NULL) {
        stats->input_bytes_consumed = pos;
    }
    *out_count = count;
    return ok && stats != NULL ? (!stats->input_truncated && !stats->output_truncated) : ok;
}

static bool wp_compact_write_byte(uint8_t *out,
                                  size_t out_capacity,
                                  size_t *count,
                                  uint8_t value,
                                  WpCompactStats *stats)
{
    if (count == NULL) {
        return false;
    }
    if (*count >= out_capacity || out == NULL) {
        if (stats != NULL) {
            stats->output_truncated = true;
        }
        return false;
    }
    out[(*count)++] = value;
    if (stats != NULL) {
        stats->bytes_written++;
    }
    return true;
}

bool wp_compact_expand_c0_escape_tokens(const uint8_t *src,
                                        size_t src_len,
                                        uint8_t *out,
                                        size_t out_capacity,
                                        size_t *out_len,
                                        WpCompactStats *stats)
{
    size_t pos = 0;
    size_t count = 0;
    bool ok = true;

    if (out_len != NULL) {
        *out_len = 0;
    }
    wp_compact_stats_clear(stats);

    if (src == NULL || out_len == NULL || (out_capacity > 0U && out == NULL)) {
        if (stats != NULL) {
            stats->input_truncated = true;
        }
        return false;
    }

    while (pos < src_len) {
        uint8_t b = src[pos];

        if (b == 0xC0U) {
            if (pos + 3U >= src_len) {
                pos = src_len;
                if (stats != NULL) {
                    stats->input_truncated = true;
                }
                ok = false;
                break;
            }
            if (out == NULL || count + 4U > out_capacity) {
                if (stats != NULL) {
                    stats->output_truncated = true;
                }
                ok = false;
                break;
            }
            out[count++] = 0xC0U;
            out[count++] = src[pos + 1U];
            out[count++] = src[pos + 2U];
            out[count++] = 0xC0U;
            if (stats != NULL) {
                stats->bytes_written += 4U;
            }
            pos += 4U;
            if (stats != NULL) {
                stats->c0_word_tokens++;
            }
            continue;
        }

        if (!wp_compact_write_byte(out, out_capacity, &count, b, stats)) {
            ok = false;
            break;
        }
        pos++;
        if (b == 0U) {
            if (stats != NULL) {
                stats->hit_terminator = true;
            }
            break;
        }
    }

    if (pos >= src_len && (stats == NULL || !stats->hit_terminator) && ok) {
        if (stats != NULL) {
            stats->input_truncated = true;
        }
        ok = false;
    }

    if (stats != NULL) {
        stats->input_bytes_consumed = pos;
    }
    *out_len = count;
    return ok && stats != NULL ? (!stats->input_truncated && !stats->output_truncated) : ok;
}
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