X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;ds=sidebyside;f=ir%2Fadt%2Fbitfiddle.h;h=e01eea3ac3fe8b404f0ebdd87c3933b0e48197b8;hb=83909ad3889884e223dcab09fddc3c77410ac15c;hp=d51b40552800b6851a712bba833690503a0b33dc;hpb=ed68ef335c85f51d542de75a52111527269860ea;p=libfirm

diff --git a/ir/adt/bitfiddle.h b/ir/adt/bitfiddle.h
index d51b40552..e01eea3ac 100644
--- a/ir/adt/bitfiddle.h
+++ b/ir/adt/bitfiddle.h
@@ -10,10 +10,41 @@
 #ifndef __FIRM_HACKDEL_H
 #define __FIRM_HACKDEL_H
 
+#include <limits.h>
+
 #include "firm_config.h"
 
 #define HACKDEL_WORDSIZE 32
 
+/**
+ * Add saturated.
+ * @param x Summand 1.
+ * @param y Summand 2.
+ * @return x + y or INT_MAX/INT_MIN if an overflow occurred and x,y was positive/negative.
+ *
+ * @note See hacker's delight, page 27.
+ */
+static INLINE int add_saturated(int x, int y)
+{
+	int sum      = x + y;
+	/*
+		An overflow occurs, if the sign of the both summands is equal
+		and the one of the sum is different from the summand's one.
+		The sign bit is 1, if an overflow occurred, 0 otherwise.
+		int overflow = ~(x ^ y) & (sum ^ x);
+	*/
+	int overflow = (x ^ sum) & (y ^ sum);
+
+	/*
+		The infinity to use.
+		Make a mask of the sign bit of x and y (they are the same if an overflow occurred).
+		INT_MIN == ~INT_MAX, so if the sign was negative, INT_MAX becomes INT_MIN.
+	*/
+	int inf      = (x >> (sizeof(x) * 8 - 1)) ^ INT_MAX;
+
+	return overflow < 0 ? inf : sum;
+}
+
 /**
  * Compute the count of set bits in a 32-bit word.
  * @param x A 32-bit word.
@@ -29,9 +60,9 @@ static INLINE unsigned popcnt(unsigned x) {
 }
 
 /**
- * Compute the number of leading zeroes in a word.
+ * Compute the number of leading zeros in a word.
  * @param x The word.
- * @return The number of leading (from the most significant bit) zeroes.
+ * @return The number of leading (from the most significant bit) zeros.
  */
 static INLINE unsigned nlz(unsigned x) {
   x |= x >> 1;
@@ -43,9 +74,9 @@ static INLINE unsigned nlz(unsigned x) {
 }
 
 /**
- * Compute the number of trailing zeroes in a word.
+ * Compute the number of trailing zeros in a word.
  * @param x The word.
- * @return The number of trailing zeroes.
+ * @return The number of trailing zeros.
  */
 #define ntz(x) (HACKDEL_WORDSIZE - nlz(~(x) & ((x) - 1)))
 
@@ -74,4 +105,5 @@ static INLINE unsigned nlz(unsigned x) {
 #define round_up2(x,pot) (((x) + ((pot) - 1)) & (~((pot) - 1)))
 
 
+
 #endif