[PATCH] libstdc++: Merge latest Ryu sources

[PATCH] libstdc++: Merge latest Ryu sources

[Patrick Palka]

The only source change is a speedup to pow5Factor.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

libstdc++-v3/ChangeLog:

	* src/c++17/ryu/MERGE: Update the commit hash.
	* src/c++17/ryu/d2s_intrinsics.h: Merge from Ryu's master
	branch.
---
 libstdc++-v3/src/c++17/ryu/MERGE            | 2 +-
 libstdc++-v3/src/c++17/ryu/d2s_intrinsics.h | 9 ++++-----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/src/c++17/ryu/MERGE b/libstdc++-v3/src/c++17/ryu/MERGE
index 0ea65add2ff..9035502846e 100644
--- a/libstdc++-v3/src/c++17/ryu/MERGE
+++ b/libstdc++-v3/src/c++17/ryu/MERGE
@@ -1,4 +1,4 @@
-22c887c017a8512abcd4a8f6bfcdb2742829cd7d
+150d0c87830756d34e76c42f7f33f811d89903a8
 
 The first line of this file holds the git revision number of the
 last merge done from the master library sources.
diff --git a/libstdc++-v3/src/c++17/ryu/d2s_intrinsics.h b/libstdc++-v3/src/c++17/ryu/d2s_intrinsics.h
index bbac4dfd48f..e3206b5d7dd 100644
--- a/libstdc++-v3/src/c++17/ryu/d2s_intrinsics.h
+++ b/libstdc++-v3/src/c++17/ryu/d2s_intrinsics.h
@@ -181,15 +181,14 @@ static inline uint32_t mod1e9(const uint64_t x) {
 #endif // defined(RYU_32_BIT_PLATFORM)
 
 static inline uint32_t pow5Factor(uint64_t value) {
+  const uint64_t m_inv_5 = 14757395258967641293u; // 5 * m_inv_5 = 1 (mod 2^64)
+  const uint64_t n_div_5 = 3689348814741910323u;  // #{ n | n = 0 (mod 2^64) } = 2^64 / 5
   uint32_t count = 0;
   for (;;) {
     assert(value != 0);
-    const uint64_t q = div5(value);
-    const uint32_t r = ((uint32_t) value) - 5 * ((uint32_t) q);
-    if (r != 0) {
+    value *= m_inv_5;
+    if (value > n_div_5)
       break;
-    }
-    value = q;
     ++count;
   }
   return count;
-- 
2.34.0

Re: [PATCH] libstdc++: Merge latest Ryu sources

[Jonathan Wakely]

On Tue, 16 Nov 2021 at 00:36, Patrick Palka wrote:
>
> The only source change is a speedup to pow5Factor.
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

OK, thanks.