From bb60877b0466007739cf6abf68f5b01ace9faeac Mon Sep 17 00:00:00 2001
From: Jeffrey Sarnoff <JeffreySarnoff@users.noreply.github.com>
Date: Mon, 3 Oct 2022 11:38:35 -0400
Subject: [PATCH] bugfix: fld1 order of ops (#46938)

* bugfix: fld1 order of ops

fixes https://github.com/JuliaLang/julia/issues/28973

(cherry picked from commit fcdc5bc21296520c04349c901e234477c5e2ffad)
---
 NEWS.md           | 1 +
 base/operators.jl | 2 +-
 test/operators.jl | 3 +++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 334517e2e9598..8e0493f8a2b12 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -147,6 +147,7 @@ Library changes
 * `RegexMatch` objects can now be probed for whether a named capture group exists within it through `haskey()` ([#36717]).
 * For consistency `haskey(r::RegexMatch, i::Integer)` has also been added and returns if the capture group
   for `i` exists ([#37300]).
+* An issue with order of operations in `fld1` is now fixed ([#28973]).
 
 Standard library changes
 ------------------------
diff --git a/base/operators.jl b/base/operators.jl
index 8120e95913e3c..154b4963b7b14 100644
--- a/base/operators.jl
+++ b/base/operators.jl
@@ -802,7 +802,7 @@ julia> x == (fld1(x, y) - 1) * y + mod1(x, y)
 true
 ```
 """
-fld1(x::T, y::T) where {T<:Real} = (m = mod1(x, y); fld(x + y - m, y))
+fld1(x::T, y::T) where {T<:Real} = (m = mod1(x, y); fld((x - m) + y, y))
 function fld1(x::T, y::T) where T<:Integer
     d = div(x, y)
     return d + (!signbit(x ⊻ y) & (d * y != x))
diff --git a/test/operators.jl b/test/operators.jl
index bdb0abcdaed1e..c584cfee7f2b5 100644
--- a/test/operators.jl
+++ b/test/operators.jl
@@ -217,6 +217,9 @@ end
     end
 
     @test fldmod1(4.0, 3) == fldmod1(4, 3)
+
+    # issue 28973
+    @test fld1(0.4, 0.9) == fld1(nextfloat(0.4), 0.9) == 1.0
 end
 
 @testset "Fix12" begin