138 lines
3.1 KiB
C
138 lines
3.1 KiB
C
#ifndef BUFFER_H
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#define BUFFER_H
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#include <stdbool.h>
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#include <unistd.h>
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/**
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* buffer.c - buffer con acceso directo (útil para I/O) que mantiene
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* mantiene puntero de lectura y de escritura.
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*
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*
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* Para esto se mantienen dos punteros, uno de lectura
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* y otro de escritura, y se provee funciones para
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* obtener puntero base y capacidad disponibles.
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*
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* R=0
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* ↓
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* +---+---+---+---+---+---+
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* | | | | | | |
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* +---+---+---+---+---+---+
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* ↑ ↑
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* W=0 limit=6
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*
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* Invariantes:
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* R <= W <= limit
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*
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* Se quiere escribir en el bufer cuatro bytes.
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*
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* ptr + 0 <- buffer_write_ptr(b, &wbytes), wbytes=6
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* n = read(fd, ptr, wbytes)
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* buffer_write_adv(b, n = 4)
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*
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* R=0
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* ↓
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* +---+---+---+---+---+---+
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* | H | O | L | A | | |
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* +---+---+---+---+---+---+
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* ↑ ↑
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* W=4 limit=6
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*
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* Quiero leer 3 del buffer
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* ptr + 0 <- buffer_read_ptr, wbytes=4
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* buffer_read_adv(b, 3);
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*
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* R=3
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* ↓
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* +---+---+---+---+---+---+
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* | H | O | L | A | | |
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* +---+---+---+---+---+---+
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* ↑ ↑
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* W=4 limit=6
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*
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* Quiero escribir 2 bytes mas
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* ptr + 4 <- buffer_write_ptr(b, &wbytes=2);
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* buffer_write_adv(b, 2)
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*
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* R=3
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* ↓
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* +---+---+---+---+---+---+
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* | H | O | L | A | | M |
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* +---+---+---+---+---+---+
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* ↑
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* limit=6
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* W=4
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* Compactación a demanda
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* R=0
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* ↓
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* +---+---+---+---+---+---+
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* | A | | M | | | |
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* +---+---+---+---+---+---+
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* ↑ ↑
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* W=3 limit=6
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*
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* Leo los tres bytes, como R == W, se auto compacta.
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*
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* R=0
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* ↓
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* +---+---+---+---+---+---+
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* | | | | | | |
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* +---+---+---+---+---+---+
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* ↑ ↑
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* W=0 limit=6
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*/
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typedef struct buffer buffer;
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struct buffer {
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uint8_t * data;
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/** límite superior del buffer. inmutable */
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uint8_t * limit;
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/** puntero de lectura */
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uint8_t * read;
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/** puntero de escritura */
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uint8_t * write;
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};
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/**
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* inicializa el buffer sin utilizar el heap
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*/
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void buffer_init(buffer * b, const size_t n, uint8_t * data);
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/**
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* Retorna un puntero donde se pueden escribir hasta `*nbytes`.
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* Se debe notificar mediante la función `buffer_write_adv'
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*/
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uint8_t * buffer_write_ptr(buffer * b, size_t * nbyte);
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void buffer_write_adv(buffer * b, const ssize_t bytes);
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uint8_t * buffer_read_ptr(buffer * b, size_t * nbyte);
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void buffer_read_adv(buffer *b, const ssize_t bytes);
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/**
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* obtiene un byte
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*/
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uint8_t buffer_read(buffer * b);
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/** escribe un byte */
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void buffer_write(buffer * b, uint8_t c);
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/**
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* compacta el buffer
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*/
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void buffer_compact(buffer * b);
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/**
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* Reinicia todos los punteros
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*/
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void buffer_reset(buffer * b);
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/** retorna true si hay bytes para leer del buffer */
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bool buffer_can_read(buffer * b);
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/** retorna true si se pueden escribir bytes en el buffer */
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bool buffer_can_write(buffer *b);
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#endif
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