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# Offers example of inline C for binary search algorithm.
# Borrowed from Kalle Svensson in the Python Cookbook.
# The results are nearly in the "not worth it" catagory.
#
# C:\home\ej\wrk\scipy\compiler\examples>python binary_search.py
# Binary search for 3000 items in 100000 length list of integers:
# speed in python: 0.139999985695
# speed in c: 0.0900000333786
# speed up: 1.41
# search(a,3450) 3450 3450
# search(a,-1) -1 -1
# search(a,10001) 10001 10001
#
# Note -- really need to differentiate between conversion errors and
# run time errors. This would reduce useless compiles and provide a
# more intelligent control of things.
import sys
sys.path.insert(0,'..')
#from compiler import inline_tools
import inline_tools
from bisect import bisect
def c_int_search(seq,t,chk=1):
# do partial type checking in Python.
# checking that list items are ints should happen in py_to_scalar<int>
if chk:
assert(type(t) == type(1))
assert(type(seq) == type([]))
code = """
#line 29 "binary_search.py"
int val, m, min = 0;
int max = seq.length()- 1;
PyObject *py_val;
for(;;)
{
if (max < min )
{
return_val = Py::new_reference_to(Py::Int(-1));
break;
}
m = (min + max) / 2;
val = py_to_int(PyList_GetItem(seq.ptr(),m),"val");
if (val < t)
min = m + 1;
else if (val > t)
max = m - 1;
else
{
return_val = Py::new_reference_to(Py::Int(m));
break;
}
}
"""
#return inline_tools.inline(code,['seq','t'],compiler='msvc')
return inline_tools.inline(code,['seq','t'],verbose = 2)
try:
from Numeric import *
def c_array_int_search(seq,t):
code = """
#line 62 "binary_search.py"
int val, m, min = 0;
int max = _Nseq[0] - 1;
PyObject *py_val;
for(;;)
{
if (max < min )
{
return_val = Py::new_reference_to(Py::Int(-1));
break;
}
m = (min + max) / 2;
val = seq_data[m];
if (val < t)
min = m + 1;
else if (val > t)
max = m - 1;
else
{
return_val = Py::new_reference_to(Py::Int(m));
break;
}
}
"""
#return inline_tools.inline(code,['seq','t'],compiler='msvc')
return inline_tools.inline(code,['seq','t'],verbose = 2,
extra_compile_args=['-O2','-G6'])
except:
pass
def py_int_search(seq, t):
min = 0; max = len(seq) - 1
while 1:
if max < min:
return -1
m = (min + max) / 2
if seq[m] < t:
min = m + 1
elif seq[m] > t:
max = m - 1
else:
return m
import time
def search_compare(a,n):
print 'Binary search for %d items in %d length list of integers:'%(n,m)
t1 = time.time()
for i in range(n):
py_int_search(a,i)
t2 = time.time()
py = (t2-t1)
print ' speed in python:', (t2 - t1)
# bisect
t1 = time.time()
for i in range(n):
bisect(a,i)
t2 = time.time()
bi = (t2-t1)
print ' speed of bisect:', bi
print ' speed up: %3.2f' % (py/bi)
# get it in cache
c_int_search(a,i)
t1 = time.time()
for i in range(n):
c_int_search(a,i,chk=1)
t2 = time.time()
print ' speed in c:',(t2 - t1)
print ' speed up: %3.2f' % (py/(t2-t1))
# get it in cache
c_int_search(a,i)
t1 = time.time()
for i in range(n):
c_int_search(a,i,chk=0)
t2 = time.time()
print ' speed in c(no asserts):',(t2 - t1)
print ' speed up: %3.2f' % (py/(t2-t1))
# get it in cache
try:
a = array(a)
c_array_int_search(a,i)
t1 = time.time()
for i in range(n):
c_array_int_search(a,i)
t2 = time.time()
print ' speed in c(Numeric arrays):',(t2 - t1)
print ' speed up: %3.2f' % (py/(t2-t1))
except:
pass
if __name__ == "__main__":
# note bisect returns index+1 compared to other algorithms
m= 100000
a = range(m)
n = 50000
search_compare(a,n)
print 'search(a,3450)', c_int_search(a,3450), py_int_search(a,3450), bisect(a,3450)
print 'search(a,-1)', c_int_search(a,-1), py_int_search(a,-1), bisect(a,-1)
print 'search(a,10001)', c_int_search(a,10001), py_int_search(a,10001),bisect(a,10001)
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