From f274dcf35aa0d3f4748387dbddfe50e8d7d44951 Mon Sep 17 00:00:00 2001 From: Sebastian Hack Date: Tue, 2 May 2006 12:23:16 +0000 Subject: [PATCH] Added add_saturated [r7675] --- ir/adt/bitfiddle.h | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/ir/adt/bitfiddle.h b/ir/adt/bitfiddle.h index d51b40552..bef1bd3f9 100644 --- a/ir/adt/bitfiddle.h +++ b/ir/adt/bitfiddle.h @@ -10,10 +10,41 @@ #ifndef __FIRM_HACKDEL_H #define __FIRM_HACKDEL_H +#include + #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. @@ -74,4 +105,5 @@ static INLINE unsigned nlz(unsigned x) { #define round_up2(x,pot) (((x) + ((pot) - 1)) & (~((pot) - 1))) + #endif -- 2.20.1