From b41d6043ff9298d806de0b5f407262b081edd470 Mon Sep 17 00:00:00 2001
From: Steve Kelly <kd2cca@gmail.com>
Date: Mon, 10 Jul 2023 10:08:28 +0100
Subject: [PATCH] A few minor perforamnce fixes (#470)
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* improve `to_uint64`

Reduces some allocations and intermediate work.

PR:
```
julia> @benchmark JLD2.to_uint64(rand(UInt8, 5))
BenchmarkTools.Trial: 10000 samples with 983 evaluations.
 Range (min … max):  58.730 ns …   1.927 μs  ┊ GC (min … max):  0.00% … 93.54%
 Time  (median):     65.484 ns               ┊ GC (median):     0.00%
 Time  (mean ± σ):   75.603 ns ± 116.148 ns  ┊ GC (mean ± σ):  10.53% ±  6.58%

     ▃▁▆█▆▂
  ▂▄▆███████▆▅▄▄▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▂▂▂▂▂▂▂▂▂▂▂▂▂ ▃
  58.7 ns         Histogram: frequency by time          117 ns <

 Memory estimate: 224 bytes, allocs estimate: 4.
```

Master:
```
julia> @benchmark JLD2.to_uint64(rand(UInt8, 5))
BenchmarkTools.Trial: 10000 samples with 981 evaluations.
 Range (min … max):  63.088 ns …  1.688 μs  ┊ GC (min … max): 0.00% … 94.44%
 Time  (median):     69.438 ns              ┊ GC (median):    0.00%
 Time  (mean ± σ):   78.976 ns ± 92.630 ns  ┊ GC (mean ± σ):  8.47% ±  6.84%

  ▂▄▅▇▇█▇▆▅▅▄▃▃▃▂▂▃▂▂▁▁                                       ▂
  ██████████████████████▇▇▆▆▇▆██▇█▇▇▇██▇▆▆▆▄▁▃▃▃▆▅▆▆▅▆▄▄▃▄▆██ █
  63.1 ns      Histogram: log(frequency) by time       130 ns <

 Memory estimate: 256 bytes, allocs estimate: 4.
```

* fix failure to const-prop in error message

this was not getting const propped, so
just mark as such

* improve type stability in show_group
---
 src/compression.jl | 11 +++++------
 src/groups.jl      | 10 +++++++---
 src/misc.jl        |  4 ++--
 3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/compression.jl b/src/compression.jl
index ff61a6d9..0d0fcc83 100644
--- a/src/compression.jl
+++ b/src/compression.jl
@@ -65,18 +65,17 @@ const ID_TO_DECOMPRESSOR = Dict(
     UInt16(32004) => (:CodecLz4, :LZ4FrameCompressor, :LZ4FrameDecompressor, "LZ4"),
 )
 
+const compressor_list_string = map(values(ID_TO_DECOMPRESSOR)) do val
+    "\n\t"*string(val[1])*"."*string(val[2])
+end
+
 issupported_filter(filter_id) = filter_id ∈ keys(ID_TO_DECOMPRESSOR)
 
 function verify_compressor(compressor)
     (compressor isa Bool || haskey(COMPRESSOR_TO_ID, nameof(typeof(compressor)))) && return
 
-    crs = map(values(ID_TO_DECOMPRESSOR)) do val
-        "\n\t"*string(val[1])*"."*string(val[2])
-    end
-
-
     throw(ArgumentError("""Unsupported Compressor
-    Supported Compressors are $(crs...)"""))
+    Supported Compressors are $(compressor_list_string...)"""))
 end
 #############################################################################################################
 # Dynamic Package Loading Logic copied from FileIO
diff --git a/src/groups.jl b/src/groups.jl
index 01ab9c10..e5f2e6f2 100644
--- a/src/groups.jl
+++ b/src/groups.jl
@@ -644,7 +644,7 @@ function show_group(io::IO, g::Group, maxnumlines::Int=10, prefix::String=" ", s
     iszero(maxnumlines) && return 0
     if g.f.n_times_opened == 0
         print(io, "  (closed)")
-        return
+        return -1
     end
 
     ks = collect(keys(g))
@@ -652,7 +652,7 @@ function show_group(io::IO, g::Group, maxnumlines::Int=10, prefix::String=" ", s
 
     if isempty(ks) && prefix == " "
         print(io, "  (no datasets)")
-        return
+        return -1
     end
 
     for i = 1:length(ks)
@@ -670,7 +670,11 @@ function show_group(io::IO, g::Group, maxnumlines::Int=10, prefix::String=" ", s
             if !isempty(newg)
                 if (maxnumlines > 1 || (islast && maxnumlines >= 2))
                     print(io, '\n')
-                    maxnumlines = show_group(io, newg, islast ? maxnumlines : maxnumlines-1, prefix*(islast ? "   " : "│  "), false)
+                    ret = show_group(io, newg, islast ? maxnumlines : maxnumlines-1, prefix*(islast ? "   " : "│  "), false)
+                    if ret < 0
+                        error("closed or empty dataset, this should not happen")
+                    end
+                    maxnumlines = ret
                     maxnumlines += islast ? 0 : 1
                 else
                     nentries = length(keys(newg))
diff --git a/src/misc.jl b/src/misc.jl
index 79f372fd..f606a358 100644
--- a/src/misc.jl
+++ b/src/misc.jl
@@ -142,9 +142,9 @@ function uintofsize(sz)
 end
 
 function to_uint64(bts::Vector{UInt8})
-    bts2 = [bts; zeros(UInt8, 8-length(bts))]
+    bts2 = append!(zeros(UInt8, 8-length(bts)), reverse(bts))
     u = zero(UInt64)
-    for b in reverse(bts2)
+    for b in bts2
         u = u << 8
         u += b
     end