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py: Make qstr hash size configurable, defaults to 2 bytes.

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This patch makes configurable, via MICROPY_QSTR_BYTES_IN_HASH, the
number of bytes used for a qstr hash.  It was originally fixed at 2
bytes, and now defaults to 2 bytes.  Setting it to 1 byte will save
ROM and RAM at a small expense of hash collisions.
This commit is contained in:
Damien George
2015-07-20 11:03:13 +00:00
parent 1e8ca3a3cf
commit c3bd9415cc
5 changed files with 44 additions and 28 deletions
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12
py/makeqstrdata.py
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@@ -37,12 +37,12 @@ codepoint2name[ord('!')] = 'bang'
codepoint2name[ord('\\')] = 'backslash'
# this must match the equivalent function in qstr.c
def compute_hash(qstr):
def compute_hash(qstr, bytes_hash):
hash = 5381
for char in qstr:
hash = (hash * 33) ^ ord(char)
# Make sure that valid hash is never zero, zero means "hash not computed"
return (hash & 0xffff) or 1
return (hash & ((1 << (8 * bytes_hash)) - 1)) or 1
def do_work(infiles):
# read the qstrs in from the input files
@@ -81,6 +81,7 @@ def do_work(infiles):
# get config variables
cfg_bytes_len = int(qcfgs['BYTES_IN_LEN'])
cfg_bytes_hash = int(qcfgs['BYTES_IN_HASH'])
cfg_max_len = 1 << (8 * cfg_bytes_len)
# print out the starte of the generated C header file
@@ -88,11 +89,11 @@ def do_work(infiles):
print('')
# add NULL qstr with no hash or data
print('QDEF(MP_QSTR_NULL, (const byte*)"\\x00\\x00%s" "")' % ('\\x00' * cfg_bytes_len))
print('QDEF(MP_QSTR_NULL, (const byte*)"%s%s" "")' % ('\\x00' * cfg_bytes_hash, '\\x00' * cfg_bytes_len))
# go through each qstr and print it out
for order, ident, qstr in sorted(qstrs.values(), key=lambda x: x[0]):
qhash = compute_hash(qstr)
qhash = compute_hash(qstr, cfg_bytes_hash)
# Calculate len of str, taking escapes into account
qlen = len(qstr.replace("\\\\", "-").replace("\\", ""))
qdata = qstr.replace('"', '\\"')
@@ -100,7 +101,8 @@ def do_work(infiles):
print('qstr is too long:', qstr)
assert False
qlen_str = ('\\x%02x' * cfg_bytes_len) % tuple(((qlen >> (8 * i)) & 0xff) for i in range(cfg_bytes_len))
print('QDEF(MP_QSTR_%s, (const byte*)"\\x%02x\\x%02x%s" "%s")' % (ident, qhash & 0xff, (qhash >> 8) & 0xff, qlen_str, qdata))
qhash_str = ('\\x%02x' * cfg_bytes_hash) % tuple(((qhash >> (8 * i)) & 0xff) for i in range(cfg_bytes_hash))
print('QDEF(MP_QSTR_%s, (const byte*)"%s%s" "%s")' % (ident, qhash_str, qlen_str, qdata))
if __name__ == "__main__":
do_work(sys.argv[1:])