From 40d6c6684861d597f8e6d76d99200734c89480ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Sat, 5 Jan 2008 23:56:07 +0100
Subject: [PATCH] (find_first_one): Optimized, using slightly larger table.
(main): Use atol, arther than atoi.
Rev: nettle/examples/eratosthenes.c:1.8
---
examples/eratosthenes.c | 48 +++++++++++++++++++++++------------------
1 file changed, 27 insertions(+), 21 deletions(-)
diff --git a/examples/eratosthenes.c b/examples/eratosthenes.c
index fd38ca7d..97abe191 100644
--- a/examples/eratosthenes.c
+++ b/examples/eratosthenes.c
@@ -112,13 +112,26 @@ vector_clear_bits (unsigned long *vector, unsigned long step,
static unsigned
find_first_one (unsigned long x)
-{
- unsigned table[0x10] =
+{
+ unsigned table[0x101] =
{
- /* 0, 1, 2, 3, 4, 5, 6, 7 */
- -1, 0, 1, 0, 2, 0, 1 , 0,
- /* 8, 9, 10, 11, 12, 13, 14, 15 */
- 3, 0, 1, 0, 2, 0, 1, 0
+ 15, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 12, 0, 0, 0, 0, 0, 0, 0,11, 0, 0, 0,10, 0, 9, 8,
+ 0, 0, 1, 0, 2, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0,
+ 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 7,
};
/* Isolate least significant bit */
@@ -127,7 +140,7 @@ find_first_one (unsigned long x)
unsigned i = 0;
#if NEED_HANDLE_LARGE_LONG
#ifndef SIZEOF_LONG
- /* Can't not be tested by the preprocessor. May generate warnings
+ /* Can not be tested by the preprocessor. May generate warnings
when long is 32 bits. */
if (BITS_PER_LONG > 32)
#endif
@@ -143,17 +156,7 @@ find_first_one (unsigned long x)
x >>= 16;
i += 16;
}
- if (x >= 0x100)
- {
- x >>= 8;
- i += 8;
- }
- if (x >= 0x10)
- {
- x >>= 4;
- i += 4;
- }
- return i + table[x & 0xf];
+ return i + table[128 + (x & 0xff) - (x >> 8)];
}
/* Returns size if there's no more bits set */
@@ -204,7 +207,7 @@ main (int argc, char **argv)
return EXIT_FAILURE;
case 'b':
{
- long arg = atoi(optarg);
+ long arg = atol(optarg);
if (arg <= 10)
{
usage();
@@ -224,7 +227,7 @@ main (int argc, char **argv)
limit = 1000;
else if (argc == 1)
{
- limit = atoi(argv[0]);
+ limit = atol(argv[0]);
if (limit < 2)
return EXIT_SUCCESS;
}
@@ -239,7 +242,10 @@ main (int argc, char **argv)
if (!block_size || block_size > size)
block_size = size;
- vector = vector_alloc (size);
+ /* FIXME: Allocates a bit for all odd numbers up to limit. Could
+ save a lot of memory by allocating space only for numbers up to
+ the square root, plus one additional block. */
+ vector = vector_alloc(size);
if (!vector)
{
fprintf(stderr, "Insufficient memory.\n");
--
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