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From 808c083fbe661207ee8f0fcd3be5096b5dc17d0d Mon Sep 17 00:00:00 2001
From: David Seifert <soap@gentoo.org>
Date: Tue, 5 Mar 2024 14:54:46 +0100
Subject: [PATCH] Fix `-Wstrict-aliasing`
* Casting a `uint64_t*` to `double*` invokes undefined behavior, since
it violates the strict aliasing rules of ISO C. Instead of casting
pointers, let's read through a union which is supported by C and
yields the same performant assembly code.
Closes: https://bugs.gentoo.org/924864
---
src/random/random.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/src/random/random.c b/src/random/random.c
index 8f2d0898aa..b5b44451ae 100644
--- a/src/random/random.c
+++ b/src/random/random.c
@@ -681,8 +681,13 @@ igraph_real_t igraph_rng_get_unif01(igraph_rng_t *rng) {
* Then we subtract 1 to arrive at the [0; 1) interval. This is fast
* but we lose one bit of precision as there are 2^53 possible doubles
* between 0 and 1. */
- uint64_t r = (igraph_i_rng_get_random_bits_uint64(rng, 52) & 0xFFFFFFFFFFFFFull) | 0x3FF0000000000000ull;
- return *(double *)(&r) - 1.0;
+ union {
+ uint64_t as_uint64_t;
+ double as_double;
+ } value;
+ value.as_uint64_t =
+ (igraph_i_rng_get_random_bits_uint64(rng, 52) & 0xFFFFFFFFFFFFFull) | 0x3FF0000000000000ull;
+ return value.as_double - 1.0;
}
}
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