nissy-core

commit 9b248f3b46d5dc0e9522ed264ef71e422a5bc5a5
parent 08d524292beed48d8a383acaee96f68cb2bd1cab
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date:   Mon, 28 Jul 2025 12:16:08 +0200

Hardcoded factorial constants

Diffstat:
M
src/utils/constants.h
 | 
16
++++++++++++++++
M
src/utils/math.h
 | 
29
++++-------------------------

2 files changed, 20 insertions(+), 25 deletions(-)
diff --git a/src/utils/constants.h b/src/utils/constants.h
@@ -11,6 +11,22 @@
 
 #define UINT8_ERROR UINT8_MAX
 
+STATIC int64_t factorial[FACTORIAL_MAX+1] = {
+	[0] = 1,
+	[1] = 1,
+	[2] = 2,
+	[3] = 6,
+	[4] = 24,
+	[5] = 120,
+	[6] = 720,
+	[7] = 5040,
+	[8] = 40320,
+	[9] = 362880,
+	[10] = 3628800,
+	[11] = 39916800,
+	[12] = 479001600,
+};
+
 STATIC int64_t binomial[12][12] = {
 	{1,  0,  0,   0,   0,   0,   0,   0,   0,  0,  0, 0},
 	{1,  1,  0,   0,   0,   0,   0,   0,   0,  0,  0, 0},
diff --git a/src/utils/math.h b/src/utils/math.h
@@ -3,7 +3,6 @@
 #define MAX(x, y) ((x) > (y) ? (x) : (y))
 #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
 
-STATIC int64_t factorial(int64_t);
 STATIC bool isperm(size_t, const uint8_t *);
 STATIC int64_t permtoindex(size_t, const uint8_t *);
 STATIC void indextoperm(int64_t, size_t, uint8_t *);
@@ -12,26 +11,6 @@ STATIC int64_t digitstosumzero(size_t, const uint8_t *, uint8_t);
 STATIC void sumzerotodigits(int64_t, size_t, uint8_t, uint8_t *);
 STATIC double intpow(double, uint64_t);
 
-STATIC int64_t
-factorial(int64_t n)
-{
-	int64_t i, ret;
-
-	if (n > FACTORIAL_MAX) {
-		LOG("Error: won't compute factorial for n=%" PRId64 " because"
-		    " it is larger than %" PRId64 "\n", n, FACTORIAL_MAX);
-		return -1;
-	}
-
-	if (n < 0)
-		return 0;
-
-	for (i = 1, ret = 1; i <= n; i++)
-		ret *= i;
-
-	return ret;
-}
-
 STATIC bool
 isperm(size_t n, const uint8_t *a)
 {
@@ -78,7 +57,7 @@ permtoindex(size_t n, const uint8_t *a)
 	for (i = 0, ret = 0; i < n; i++) {
 		for (j = i+1, c = 0; j < n; j++)
 			c += (a[i] > a[j]) ? 1 : 0;
-		ret += factorial(n-i-1) * c;
+		ret += factorial[n-i-1] * c;
 	}
 
 	return ret;
@@ -99,15 +78,15 @@ indextoperm(int64_t p, size_t n, uint8_t *r)
 
 	memset(a, 0, n);
 
-	if (p < 0 || p >= factorial(n))
+	if (p < 0 || p >= factorial[n])
 		goto indextoperm_error;
 
 	for (i = 0; i < n; i++) {
-		for (j = 0, c = 0; c <= p / factorial(n-i-1); j++)
+		for (j = 0, c = 0; c <= p / factorial[n-i-1]; j++)
 			c += a[j] ? 0 : 1;
 		r[i] = j-1;
 		a[j-1] = 1;
-		p %= factorial(n-i-1);
+		p %= factorial[n-i-1];
 	}
 
 	if (!isperm(n, r))