13. A decompression process of executable code by a microprocessor, saved in a program memory zone in compressed form, the process comprising steps: receiving from the microprocessor instruction requests of executable code comprising an instruction address to be executed, determining a reading address of an addressing table as a function of the instruction address to be executed, reading to the reading address in the addressing table addressing information of compressed words corresponding to the instruction to be executed, determining as a function of the addressing information read a reading address of the program memory, reading the program memory to the reading address, and decompressing the read words and transmitting them to the microprocessor, wherein each word of the executable code is compressed in the form of a part of predefined fixed length and a part of variable length whereof the length is defined by the part of fixed length, all the parts of fixed length and all the parts of variable length of the words of executable code being combined respectively into a block of parts of fixed length and into a block of parts of variable length, at least certain parts of variable length being localized a in the block of parts of variable length by means of an addressing table, the decompression process further comprising: determining a reading address in the block of parts of fixed length as a function of the address of the instruction to be executed, reading the blocks of parts of fixed and variable length to the determined reading addresses, and decompressing the read parts of fixed and variable length to produce an executable instruction which is transmitted to the microprocessor.
13. A decompression process of executable code by a microprocessor, saved in a program memory zone in compressed form, the process comprising steps: receiving from the microprocessor instruction requests of executable code comprising an instruction address to be executed, determining a reading address of an addressing table as a function of the instruction address to be executed, reading to the reading address in the addressing table addressing information of compressed words corresponding to the instruction to be executed, determining as a function of the addressing information read a reading address of the program memory, reading the program memory to the reading address, and decompressing the read words and transmitting them to the microprocessor, wherein each word of the executable code is compressed in the form of a part of predefined fixed length and a part of variable length whereof the length is defined by the part of fixed length, all the parts of fixed length and all the parts of variable length of the words of executable code being combined respectively into a block of parts of fixed length and into a block of parts of variable length, at least certain parts of variable length being localized a in the block of parts of variable length by means of an addressing table, the decompression process further comprising: determining a reading address in the block of parts of fixed length as a function of the address of the instruction to be executed, reading the blocks of parts of fixed and variable length to the determined reading addresses, and decompressing the read parts of fixed and variable length to produce an executable instruction which is transmitted to the microprocessor. 14. The decompression process as claimed in claim 13 , in which the compressed code is organized into lines of parts of fixed length and into lines of parts of variable length, each line of parts of fixed length and the associated line of parts of variable length corresponding to a respective line of a predefined number of instructions of executable code, each of the lines of parts of variable lengths being localized in the program memory zone by means of the addressing table, the process comprising: reading a line of parts of fixed length and a line of parts of variable length, localized by means of the information read in the addressing table, and decompressing the lines of read parts of fixed and variable length to produce a line of executable instructions.