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py: Add MICROPY_QSTR_BYTES_IN_LEN config option, defaulting to 1.

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This new config option sets how many fixed-number-of-bytes to use to
store the length of each qstr.  Previously this was hard coded to 2,
but, as per issue #1056, this is considered overkill since no-one
needs identifiers longer than 255 bytes.

With this patch the number of bytes for the length is configurable, and
defaults to 1 byte.  The configuration option filters through to the
makeqstrdata.py script.

Code size savings going from 2 to 1 byte:
- unix x64 down by 592 bytes
- stmhal down by 1148 bytes
- bare-arm down by 284 bytes

Also has RAM savings, and will be slightly more efficient in execution.
This commit is contained in:
Damien George
2015-01-11 22:27:30 +00:00
parent 6942f80a8f
commit 95836f8439
4 changed files with 41 additions and 17 deletions
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32
py/qstr.c
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@@ -50,9 +50,17 @@
// - \0 terminated (for now, so they can be printed using printf)
#define Q_GET_HASH(q) ((q)[0] | ((q)[1] << 8))
#define Q_GET_ALLOC(q) (4 + Q_GET_LENGTH(q) + 1)
#define Q_GET_LENGTH(q) ((q)[2] | ((q)[3] << 8))
#define Q_GET_DATA(q) ((q) + 4)
#define Q_GET_ALLOC(q) (2 + MICROPY_QSTR_BYTES_IN_LEN + Q_GET_LENGTH(q) + 1)
#define Q_GET_DATA(q) ((q) + 2 + MICROPY_QSTR_BYTES_IN_LEN)
#if MICROPY_QSTR_BYTES_IN_LEN == 1
#define Q_GET_LENGTH(q) ((q)[2])
#define Q_SET_LENGTH(q, len) do { (q)[2] = (len); } while (0)
#elif MICROPY_QSTR_BYTES_IN_LEN == 2
#define Q_GET_LENGTH(q) ((q)[2] | ((q)[3] << 8))
#define Q_SET_LENGTH(q, len) do { (q)[2] = (len); (q)[3] = (len) >> 8; } while (0)
#else
#error unimplemented qstr length decoding
#endif
// this must match the equivalent function in makeqstrdata.py
mp_uint_t qstr_compute_hash(const byte *data, mp_uint_t len) {
@@ -143,23 +151,21 @@ qstr qstr_from_strn(const char *str, mp_uint_t len) {
qstr q = qstr_find_strn(str, len);
if (q == 0) {
mp_uint_t hash = qstr_compute_hash((const byte*)str, len);
byte *q_ptr = m_new(byte, 4 + len + 1);
byte *q_ptr = m_new(byte, 2 + MICROPY_QSTR_BYTES_IN_LEN + len + 1);
q_ptr[0] = hash;
q_ptr[1] = hash >> 8;
q_ptr[2] = len;
q_ptr[3] = len >> 8;
memcpy(q_ptr + 4, str, len);
q_ptr[4 + len] = '\0';
Q_SET_LENGTH(q_ptr, len);
memcpy(q_ptr + 2 + MICROPY_QSTR_BYTES_IN_LEN, str, len);
q_ptr[2 + MICROPY_QSTR_BYTES_IN_LEN + len] = '\0';
q = qstr_add(q_ptr);
}
return q;
}
byte *qstr_build_start(mp_uint_t len, byte **q_ptr) {
assert(len <= 65535);
*q_ptr = m_new(byte, 4 + len + 1);
(*q_ptr)[2] = len;
(*q_ptr)[3] = len >> 8;
assert(len < (1 << (8 * MICROPY_QSTR_BYTES_IN_LEN)));
*q_ptr = m_new(byte, 2 + MICROPY_QSTR_BYTES_IN_LEN + len + 1);
Q_SET_LENGTH(*q_ptr, len);
return Q_GET_DATA(*q_ptr);
}
@@ -170,7 +176,7 @@ qstr qstr_build_end(byte *q_ptr) {
mp_uint_t hash = qstr_compute_hash(Q_GET_DATA(q_ptr), len);
q_ptr[0] = hash;
q_ptr[1] = hash >> 8;
q_ptr[4 + len] = '\0';
q_ptr[2 + MICROPY_QSTR_BYTES_IN_LEN + len] = '\0';
q = qstr_add(q_ptr);
} else {
m_del(byte, q_ptr, Q_GET_ALLOC(q_ptr));