trac #4939 -- massive performance regression to primes_first_n

src/sage/rings/arith.py

@@ -523,13 +523,8 @@ def primes_first_n(n, leave_pari=False):
     Return the first $n$ primes.
 
     INPUT:
-        leave_pari -- bool (default: False) if True the returned list
-                    is a PARI list; this is *vastly* (10 times!)
-                    faster since the time of prime_range is dominated
-                    by conversion from PARI to SAGE integers.
-                    However, PARI integers are much different than
-                    SAGE integers.  If you use this option the lower
-                    bound must be 2.
+        n -- a nonnegative integer
+
     OUTPUT:
         a list of the first $n$ prime numbers.
 
@@ -538,13 +533,14 @@ def primes_first_n(n, leave_pari=False):
         [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
         sage: len(primes_first_n(1000))
         1000
-
-    This is very fast, because we leave the output as a PARI object:
-        sage: v = primes_first_n(10^6, leave_pari=True)
-        sage: len(v)
-        1000000
+        sage: primes_first_n(0)
+        []
     """
-    return fast_arith.prime_range(pari.nth_prime(n)+1, leave_pari=leave_pari)
+    if n < 0:
+        raise ValueError, "n must be nonnegative"
+    if n < 1:
+        return []
+    return fast_arith.prime_range(pari.nth_prime(n) + 1)
 
 #
 # This is from

src/sage/rings/fast_arith.pyx

@@ -53,7 +53,7 @@ from sage.rings.integer cimport Integer
 cdef extern from "convert.h":
     cdef void t_INT_to_ZZ(mpz_t value, long *g)
 
-cpdef prime_range(start, stop=None, leave_pari=False):
+cpdef prime_range(start, stop=None):
     r"""
     List of all primes between start and stop-1, inclusive.  If the
     second argument is omitted, returns the primes up to the first
@@ -66,8 +66,6 @@ cpdef prime_range(start, stop=None, leave_pari=False):
     INPUT:
         start -- lower bound
         stop -- upper bound
-        leave_pari -- (default: False) if True, return a list of Pari
-                      integers instead of Sage integers.
 
     EXAMPLES:
         sage: prime_range(10)
@@ -88,16 +86,6 @@ cpdef prime_range(start, stop=None, leave_pari=False):
     TESTS:
         sage: len(prime_range(25000,2500000))
         180310
-        sage: prime_range(8,leave_pari=True)
-        [2, 3, 5, 7]
-        sage: type(prime_range(7,leave_pari=True)[0])
-        <type 'sage.libs.pari.gen.gen'>
-        sage: prime_range(2,2,leave_pari=True)
-        []
-        sage: prime_range(2,3,leave_pari=True)
-        [2]
-        sage: prime_range(5,10,leave_pari=True)
-        [5, 7]
 
     AUTHORS:
       - William Stein (original version)
@@ -118,9 +106,6 @@ cpdef prime_range(start, stop=None, leave_pari=False):
         m = int(ZZ(pari(start-1).primepi()))
     n = lg(v.g) - 1
 
-    if leave_pari:
-        return v[m:]
-
     res = [0] * (n-m)
     for ind from m <= ind < n:
         tmp = PY_NEW(Integer)