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OCaml 4.14.0

This page describes OCaml version 4.14.0, released on 2022-03-28. Go here for a list of all releases.

This release is available as an opam package.

As the last version of OCaml 4, the 4.14 branch of OCaml will be maintained during the transition period for OCaml 5. During this period, OCaml 4.14 will receive episodic bugfix updates as a long term support branch until at least 2024.

What's new

Some of the highlights in OCaml 4.14.0 are:

  • Integrated support for "go to definitions" in Merlin.
  • Standard library: new modules In_channel and Out_channel, many new functions in Seq module, UTF decoding and validation support for strings and bytes.
  • Runtime optimisation: GC prefetching. Benchmarks show a speedup of around 20% in GC-heavy programs.
  • Improved error messages in particular for module-level error.
  • Deprecated functions and modules in preparation for OCaml 5. In particular, the Stream and Genlex modules are now deprecated.
  • Type variables can be explicitly introduced in value and variant constructor declarations. For instance,
    val fold: ('acc -> 'elt -> 'acc) -> 'acc -> 'elt list -> 'acc
    type showable = Show: 'a * ('a -> string) -> showable

can now be written as

    val fold: 'acc 'elt. ('acc -> 'elt -> 'acc) -> 'acc -> 'elt list -> 'acc
    type showable = Show: 'a. 'a * ('a -> string) -> showable
  • Tail-call with up to 64 arguments are now guaranteed to be optimized for all architectures.
  • Experimental tail modulo cons (TMC) transformation

For a comprehensive list of changes and details on all new features, bug fixes, optimizations, etc., please consult the changelog.

Configuration options

The configuration of the installed opam switch can be tuned with the following options:

  • ocaml-option-32bit: set OCaml to be compiled in 32-bit mode for 64-bit Linux and OS X hosts
  • ocaml-option-afl: set OCaml to be compiled with afl-fuzz instrumentation
  • ocaml-option-bytecode-only: compile OCaml without the native-code compiler
  • ocaml-option-default-unsafe-string: set OCaml to be compiled without safe strings by default
  • ocaml-option-flambda: set OCaml to be compiled with flambda activated
  • ocaml-option-fp: set OCaml to be compiled with frame-pointers enabled
  • ocaml-option-musl: set OCaml to be compiled with musl-gcc
  • ocaml-option-nnp : set OCaml to be compiled with --disable-naked-pointers
  • ocaml-option-nnpchecker: set OCaml to be compiled with --enable-naked-pointers-checker
  • ocaml-option-no-flat-float-array: set OCaml to be compiled with --disable-flat-float-array
  • ocaml-option-static :set OCaml to be compiled with musl-gcc -static

For instance, one can install a switch with both flambda and the naked-pointer checker enabled with

opam switch create 4.14.0+flambda+nnpchecker --package=ocaml-variants.4.14.0+options,ocaml-option-flambda,ocaml-option-nnpchecker

or with opam 2.1:

opam switch create 4.14.0+flambda+nnpchecker ocaml-variants.4.14.0+options ocaml-option-flambda ocaml-option-nnpchecker

Source distribution

  • Source tarball (.tar.gz) for compilation under Unix (including Linux and MacOS X) and Microsoft Windows (including Cygwin).
  • Also available in .zip format.
  • OPAM is a source-based distribution of OCaml and many companion libraries and tools. Compilation and installation are automated by powerful package managers.
  • The official development repo is hosted on GitHub.

The INSTALL file of the distribution provides detailed compilation and installation instructions — see also the Windows release notes for instructions on how to build under Windows.

Alternative Compilers

Additionally, the following projects allow you to compile OCaml code to targets traditionally associated with other languages:

  • Js_of_ocaml is a stable OCaml to JavaScript compiler.

User's manual

The user's manual for OCaml can be:


This is the changelog. (Changes that can break existing programs are marked with a "breaking change" warning)

Language features (highlights):

  • #10437: Allow explicit binders for type variables. (Stephen Dolan, review by Leo White)

  • #181, #9760, #10740: opt-in tail-modulo-cons (TMC) transformation let[@tail_mod_cons] rec map f li = ... (Frédéric Bour, Gabriel Scherer, Basile Clément, review by Basile Clément and Pierre Chambart, tested by Konstantin Romanov)

Runtime system (highlights):

  • #10195, #10680: Speed up GC by prefetching during marking (Stephen Dolan, review by Xavier Leroy, Guillaume Munch-Maccagnoni, Jacques-Henri Jourdan, Damien Doligez and Leo White)

Code generation and optimizations (highlights):

  • #10595: Tail calls with up to 64 arguments are guaranteed to be compiled as tail calls. To this end, memory locations in the domain state are used for passing arguments that do not fit in registers. (Xavier Leroy, review by Vincent Laviron)

Standard library (highlights):

  • (breaking change) #10710: Add UTF tools, codecs and validations to the Uchar, Bytes and String modules. (Daniel Bünzli, review by Florian Angeletti, Nicolás Ojeda Bär, Alain Frisch and Gabriel Scherer)

  • (breaking change) #10482: mark the Stream and Genlex modules as deprecated, in preparation for a future removal. These modules (without deprecation alert) are now provided by the camlp-streams library. (Xavier Leroy, review by Nicolás Ojeda Bär)

  • #10545: Add In_channel and Out_channel modules. (Nicolás Ojeda Bär, review by Daniel Bünzli, Simon Cruanes, Gabriel Scherer, Guillaume Munch-Maccagnoni, Alain Frisch and Xavier Leroy)

Compiler user-interface and warnings (highlights)

  • #10328, #10780: Give more precise error when disambiguation could not possibly work. (Leo White, review by Gabriel Scherer and Florian Angeletti)

  • #10361: Improve error messages for mismatched record and variant definitions. (Florian Angeletti, review by Gabriel Radanne and Gabriel Scherer)

  • #10407: Produce more detailed error messages that contain full error traces when module inclusion fails. (Antal Spector-Zabusky, review by Florian Angeletti)

Internal/compiler-libs changes (highlights):

  • #10718, #11012: Add "Shape" information to the cmt files. Shapes are an abstraction of modules that can be used by external tooling to perform definition-aware operations. (Ulysse Gérard, Thomas Refis and Leo White, review by Florian Angeletti)

Language features:

  • #10462: Add attribute to produce a compiler error for polls. (Sadiq Jaffer, review by Mark Shinwell, Stephen Dolan and Guillaume Munch-Maccagnoni)

  • #10441: Remove unnecessary parentheses surrounding immediate objects. Allow 'object ... end # f', 'f object ... end', etc. (Yan Dong, review by Nicolás Ojeda Bär, Florian Angeletti and Gabriel Scherer)

Runtime system:

  • (breaking change) #9391, #9424: Fix failed assertion in runtime due to ephemerons set_ and blit_ function during Mark phase (François Bobot, reported by Stephen Dolan, reviewed by Damien Doligez)
  • #10549: Stack overflow detection and naked pointers checking for ARM64 (Xavier Leroy, review by Stephen Dolan)
  • (breaking change) #10675, #10937: Emit deprecation warnings when old C runtime function names are used. This will break C stub code that uses these old names and treats warnings as errors. The workaround is to use the new names. (Xavier Leroy and David Allsopp, review by Sébastien Hinderer and Damien Doligez)
  • #10698, #10726, #10891: Free the alternate signal stack when the main OCaml code or an OCaml thread stops (Xavier Leroy, review by David Allsopp and Damien Doligez)

  • #10730, 10731: Fix bug in Obj.reachable_words causing a slowdown when called multiple time (Alain Frisch, report by ygrek, review by Xavier Leroy)

Code generation and optimizations:

  • #10578: Increase the number of integer registers used for parameter passing on PowerPC (16 registers) and on s390x (8 registers). (Xavier Leroy, review by Mark Shinwell)

  • #10591, #10615: Tune the heuristic for CSE of integer constants so as to avoid excessive CSE on compiler-generated constants and long register allocation times. (Xavier Leroy, report by Edwin Török, review by Nicolás Ojeda Bär)

  • #10681: Enforce boolean conditions for the native backend (Vincent Laviron, review by Gabriel Scherer)

  • #10719: Ensure that build_apply respects Lambda.max_arity (Stephen Dolan, review by Xavier Leroy)

  • #10728: Ensure that functions are evaluated after their arguments (Stephen Dolan, review by Mark Shinwell)

  • #10732: Ensure right-to-left evaluation of arguments in cmm_helpers (Greta Yorsh, review by Xavier Leroy)

Standard library:

  • (breaking change) #10622: Annotate Uchar.t with immediate attribute (Hongbo Zhang, reivew by Gabriel Scherer and Nicolás Ojeda Bär)

  • (breaking change) #7812, #10475: Filename.chop_suffix name suff now checks that suff is actually a suffix of name and raises Invalid_argument otherwise. (Xavier Leroy, report by whitequark, review by David Allsopp)

  • #10526: add Random.bits32, Random.bits64, Random.nativebits (Xavier Leroy, review by Gabriel Scherer and François Bobot)
  • (breaking change) #10568: remove Obj.marshal and Obj.unmarshal (these functions have been deprecated for a while and are superseded by the functions from module Marshal) (François Pottier, review by Gabriel Scherer and Kate Deplaix)
  • #10538: add Out_channel.set_buffered and Out_channel.is_buffered to control the buffering mode of output channels. (Nicolás Ojeda Bär, review by John Whitington, Daniel Bünzli, David Allsopp and Xavier Leroy)
  • (breaking change) #10583, #10998: Add over 40 new functions in Seq. (François Pottier and Simon Cruanes, review by Nicolás Ojeda Bär, Daniel Bünzli, Naëla Courant, Craig Ferguson, Wiktor Kuchta, Xavier Leroy, Guillaume Munch-Maccagnoni, Raphaël Proust, Gabriel Scherer and Thierry Martinez)
  • #10596, #10978: Add with_open_bin, with_open_text and with_open_gen to In_channel and Out_channel. Also, add In_channel.input_all. (Nicolás Ojeda Bär, review by Daniel Bünzli, Jérémie Dimino, Damien Doligez and Xavier Leroy)

  • #10658: add detailed information about the current version of OCaml to the Sys module of the standard library. (Sébastien Hinderer, review by Damien Doligez, Gabriel Scherer, David Allsopp, Nicolás Ojeda Bär, Vincent Laviron)

  • #10642: On Windows, Sys.remove and Unix.unlink now remove symlinks to directories instead of raising EACCES. Introduce caml/winsupport.h to hold more common code between the runtime, lib-sys, and win32unix. (Antonin Décimo, review by David Allsopp and Xavier Leroy)

  • #10737: add new ephemeron API for forward compatibility with Multicore OCaml. (Damien Doligez, review by Stephen Dolan)

  • (breaking change) #10922: Add deprecation warnings on {Int32,Int64,Nativeint}.format. (Nicolás Ojeda Bär, review by Xavier Leroy and Florian Angeletti)

Other libraries:

  • #10192: Add support for Unix domain sockets on Windows and use them to emulate Unix.socketpair (only available on Windows 1803+) (Antonin Décimo, review by David Allsopp)

  • #10469: Add Thread.set_uncaught_exception_handler and Thread.default_uncaught_exception_handler. (Enguerrand Decorne, review by David Allsopp)

  • #10697: Bindings of dup and dup2 in win32unix now correctly call WSADuplicateSocket on sockets instead of DuplicateHandle. (Antonin Décimo, review by Xavier Leroy and Nicolás Ojeda Bär)

  • #10951: Introduce the Thread.Exit exception as an alternative way to terminate threads prematurely. This alternative way will become the standard way in 5.00. (Xavier Leroy, review by Florian Angeletti)


  • #10839: Fix regression of #show when printing class type (Élie Brami, review by Florian Angeletti)

  • #3959, #7202, #10476: ocaml, in script mode, directive errors (#use "missing_file";;) use stderr and exit with an error. (Florian Angeletti, review by Gabriel Scherer)

  • #10438: add a new toplevel cli argument -e <script> to run script passed to the toplevel. (Pavlo Khrystenko, review by Gabriel Scherer)

  • #10524: Directive argument type error now shows expected and received type. (Wiktor Kuchta, review by Gabriel Scherer)

  • #10560: Disable colors if the env variable NO_COLOR is set. If OCAML_COLOR is set, its setting takes precedence over NO_COLOR. (Nicolás Ojeda Bär, report by Gabriel Scherer, review by Daniel Bünzli, Gabriel Scherer and David Allsopp)

  • #10565: Toplevel value printing: truncate strings only after 8 bytes. (Wiktor Kuchta, review by Xavier Leroy)

  • #10527: Show "#help;; for help" at toplevel startup (Wiktor Kuchta, review by David Allsopp and Florian Angeletti)

  • #10846: add the -shape command-line option to ocamlobjinfo. When reading a cmt file, shape information will only be shown if that option is used. (Ulysse Gérard, review by Florian Angeletti)


  • #10517, #10594: when running ocamldebug on a program linked with the threads library, don't fail immediately; instead, allow debugging until the program creates a thread for the first time, then fail cleanly. (Xavier Leroy, report by @anentropic, review by Gabriel Scherer)

  • #9621: Pack the ocamldebug modules to minimize clashes (Raphael Sousa Santos, review by Vincent Laviron and Gabriel Scherer)

Manual and documentation:

  • #7812, #10475: reworded the description of the behaviors of float->int conversions in case of overflow, and of iterators in case of concurrent modifications. (Xavier Leroy, report by whitequark, review by David Allsopp)

  • #8697, #10666: add M, m, n options of the OCAMLRUNPARAM to manual and man page for ocamlrun command line options (Dong An and Anukriti Kumar, review by David Allsopp, Gabriel Scherer and Damien Doligez)

  • #10281, #10685: Add description of C compiler on macOS and Windows platforms. (Dong An, review by Xavier Leroy and David Allsopp)

  • #10397: Document exceptions raised by Unix module functions on Windows (Martin Jambon, review by Daniel Bünzli, David Alsopp, Damien Doligez, Xavier Leroy, and Florian Angeletti)

  • #10589: Fix many typos (excess/inconsistent spaces) in the HTML manual. (Wiktor Kuchta, review by Florian Angeletti)

  • #10605: manual, name few css classes to ease styling and maintainability. (Florian Angeletti, review by Wiktor Kuchta and Gabriel Scherer)

  • #10668, #10669: the changelog (this file), LICENSE and README files are now installed as part of the distribution. The destination directory can be customized using the --docdir argument to ./configure. (Nicolás Ojeda Bär, report by Daniel Bünzli, review by David Allsopp, Sébastien Hinderer, and Daniel Bünzli)

  • #10671, #10672: webman: Fix misalignments in unordered lists by changing the CSS for coloring bullets (Wiktor Kuchta, review by Florian Angeletti)

  • #11107: Lifted comments in the Parsetree module into actual documentation. (Paul-Elliot Anglès d'Auriac, review by Florian Angeletti)

  • #11120, #11133: man pages, add missing warning entries and add mnemonic names to the list of warnings. (Florian Angeletti, report by Kate Deplaix, review by Gabriel Scherer)

Compiler user-interface and warnings:

  • #10531: add naked_pointers to ocamlc -config exporting NAKED_POINTERS from Makefile.config. (Damien Doligez, review by Mark Shinwell and Gabriel Scherer)

  • #9116, #9118, #10582: Fix single-line source highlighting in the presence of tabs (Armaël Guéneau, review by Gabriel Scherer, split off from #9118 by Kate Deplaix, report by Ricardo M. Correia)

  • #10488: Improve type variable name generation and recursive type detection when printing type errors; this ensures that the names given to type variables are always reused in the following portion of the trace and also removes spurious as 'as in types. (Antal Spector-Zabusky, review by Florian Angeletti)

  • #10794: Clarify warning 57 (Ambiguous or-pattern variables under guard) (Wiktor Kuchta, review by Gabriel Scherer)

Internal/compiler-libs changes:

  • #1599: add unset directive to ocamltest to clear environment variables before running tests. (David Allsopp, review by Damien Doligez and Sébastien Hinderer)

  • #8516: Change representation of class signatures (Leo White, review by Thomas Refis)

  • #9444: -dtypedtree, print more explictly extra nodes in pattern ast. (Frédéric Bour, review by Gabriel Scherer)

  • #10337: Normalize type_expr nodes on access One should now use accessors such as get_desc and get_level to access fields of type_expr, rather than calling manually Btype.repr (which is now hidden in Types.Transient_expr). (Jacques Garrigue and Takafumi Saikawa, review by Florian Angeletti and Gabriel Radanne)

  • #10474: Force normalization on access to row_desc Similar to #10337. Make row_desc an abstract types, with constructor create_row and accessors defined in Types rather than Btype. A normalized view row_desc_repr is provided for convenience. (Jacques Garrigue and Takafumi Saikawa, review by Leo White and Florian Angeletti)

  • #10541: Make field_kind and commutable abstract, enforcing correct access (Jacques Garrigue and Takafumi Saikawa, review by Thomas Refis and Florian Angeletti)

  • #10575: add a -dump-dir flag, which redirects all debugging printer (-dprofile, -dlambda, ...) to the target directory (Florian Angeletti, review by Thomas Refis and Gabriel Scherer)

  • (breaking change) #10627: Make row_field abstract Completes #10474 by making row_field abstract too. An immutable view row_field_view is provided, and one converts between it and row_field via inj_row_field and row_field_repr. (Jacques Garrigue and Takafumi Saikawa, review by Florian Angeletti)
  • #10433: Remove the distinction between 32-bit aligned and 64-bit aligned 64-bit floats in Cmm.memory_chunk. (Greta Yorsh, review by Xavier Leroy)

  • #10434: Pun labelled arguments with type constraint in function applications. (Greta Yorsh, review by Nicolas Chataing and Nicolás Ojeda Bär)

  • #10470: Remove unused cstr_normal field from the constructor_description type (Nicolas Chataing, review by Gabriel Scherer)

  • #10382: Don't repeat environment entries in Typemod.check_type_decl (Leo White, review by Gabriel Scherer and Florian Angeletti)

  • #10472: refactor caml_sys_random_seed to ease future Multicore changes (Gabriel Scherer, review by Xavier Leroy)

  • #10487: Move logic to get the type path from a constructor return type in Types (Nicolas Chataing, review by Jacques Garrigue)

  • #10555: Do not use ghost locations for type constraints (Nicolás Ojeda Bär, report by Anton Bachin, review by Thomas Refis)

  • #10598, #10616: fix an exponential blow-up when typechecking nested module types (Florian Angeletti, report and review by Stephen Dolan)

  • #10559: Evaluate signature substitutions lazily (Stephen Dolan, review by Leo White)

  • #8776, #10624: Fix compilation time regression introduced in 4.08 (Nicolás Ojeda Bär, fix by Leo White, report by Alain Frisch, review by Thomas Refis)

  • #10618: Expose more Pprintast functions (Guillaume Petiot, review by Gabriel Scherer)

  • #10637: Outcometree: introduce a record type for constructors (Gabriel Scherer, review by Thomas Refis)

  • #10516: refactor the compilation of the 'switch' construct (Gabriel Scherer, review by Wiktor Kuchta and Luc Maranget)

  • #10670: avoid global C state in the RE engine for the "str" library (Xavier Leroy, review by Gabriel Scherer)

  • #10678: Expose descriptions in Warnings module (Leo White, review by Gabriel Scherer and Alain Frisch)

  • #10690: Always build ocamltoplevel.cmxa (David Allsopp, review by Gabriel Scherer)

  • #10692: Expose Parse.module_type and Parse.module_expr (Guillaume Petiot, review by Gabriel Scherer)

  • #10714: Add X86_proc.with_internal_assembler for temporarily changing the assembler used by the backend. (David Allsopp, review by Gabriel Scherer)

  • #10715: Allow the assembler and loader to be substituted in ocamlnat, for example to be replaced with a binary emitter. (David Allsopp and Nathan Rebours, review by Louis Gesbert, Nicolás Ojeda Bär and Gabriel Scherer)

  • #10742: strong call-by-need reduction for shapes (Gabriel Scherer and Nathanaëlle Courant, review by Florian Angeletti, Ulysse Gérard and Thomas Refis)

Build system:

  • #10828 Build native-code compilers on OpenBSD/aarch64 (Christopher Zimmermann)

  • #10835 Disable DT_TEXTREL warnings on x86 32 bit architecture by passing -Wl,-z,notext in mksharedlib and mkmaindll. Fixes relocation issues, reported in #9800, making local patches in Debian, Alpine, and FreeBSD superfluous. (Hannes Mehnert with Kate Deplaix and Stéphane Glondu, review by Xavier Leroy)

  • #10717: Simplify the installation of man pages (Sébastien Hinderer, review by David Allsopp)

  • #10739: Stop installing extract_crc (Sébastien Hinderer, review by David Allsopp, Daniel Bünzli, Xavier Leroy and Gabriel Scherer)

  • #10797: Compile with -d2VolatileMetadata- on supporting versions of Visual Studio. This suppresses the addition of .voltbl sections and eliminates linking errors in systhreads. (David Allsopp, review by Jonah Beckford and Sébastien Hinderer)

Bug fixes:

  • #9214, #10709: Wrong unmarshaling of function pointers in debugger mode. This was causing ocamldebug to crash when running some user-defined printers. (Xavier Leroy, report by Rehan Malak, review by Gabriel Scherer and Vincent Laviron)

  • #10473: Add CFI directives to RISC-V runtime and asmcomp. This allows stacktraces to work in gdb through C and OCaml calls. (Edwin Török, review by Nicolás Ojeda Bär and Xavier Leroy)

  • #10539: Field kinds should be kept when copying types Losing the sharing meant that one could desynchronize them between several occurrences of self, allowing a method to be both public and hidden, which broke type soundness. (Jacques Garrigue, review by Leo White)

  • #10542: Fix detection of immediate64 types through unboxed types. (Leo White, review by Stephen Dolan and Gabriel Scherer)

  • #10590: Some typechecker optimisations (Stephen Dolan, review by Gabriel Scherer and Leo White)

  • #10633: Stack overflow recovery in ocamlopt for AMD64/Linux and ARM/Linux was not restoring the minor heap pointer correctly (Stephen Dolan, review by Xavier Leroy)

  • #10659: Fix freshening substitutions on imported modules (Leo White and Stephen Dolan, review by Matthew Ryan)

  • #10677, #10679: Fix detection of CC as gcc in configure (allow for triplet-prefixed GCC) and fix all C compiler detection when CC is a path rather than a basename. (David Allsopp, report by Fabian @copy, review by Gabriel Scherer)

  • #10690: Add --enable-native-toplevel to configure to enable installing ocamlnat as part of the main build (default is not to install it) (David Allsopp, review by Gabriel Scherer)

  • #10693: Fix ident collision in includemod (Leo White, review by Matthew Ryan)

  • #10702: Fix cast of more strictly aligned pointer in win32unix implementation of stat (Antonin Décimo, review by David Allsopp)

  • #10712: Type-check toplevel terms in the native toplevel in the same way as the bytecode toplevel. In particular, this fixes the loss of type variable names in the native toplevel. (Leo White, review by David Allsopp and Gabriel Scherer)

  • #10735: Uncaught unify exception from build_as_type (Jacques Garrigue, report and review by Leo White)

  • #10763, #10764: fix miscompilation of method delegation (Alain Frisch, review by Vincent Laviron and Jacques Garrigue)

  • #10822, #10823: Bad interaction between ambivalent types and subtyping coercions (Jacques Garrigue, report and review by Frédéric Bour)

  • #10836, #10952: avoid internal typechecker errors when checking signature inclusion in presence of incompatible types. (Florian Angeletti, report by Craig Ferguson, review by Gabriel Scherer)

  • #10849: Display the result of let _ : <type> = <expr> in the native toplevel, as in the bytecode toplevel. (David Allsopp, report by Nathan Rebours, review by Gabriel Scherer)

  • #10853: Obj.reachable_words could crash if called after a marshaling operation in NO_SHARING mode. (Xavier Leroy, report by Anil Madhavapeddy, review by Alain Frisch)

  • #10907, #10959: Wrong type inferred from existential types (Jacques Garrigue and Gabriel Scherer, report by @dyzsr, review by Leo White)

  • #10688: Move frame descriptor table from rodata to data section on RISC-V. Improves support for building DLLs and PIEs. In particular, this applies to all binaries in distributions that build PIEs by default (eg Gentoo and Alpine). (Alex Fan, review by Gabriel Scherer)

  • #11031: Exception handlers restore the rbp register when using frame-pointers on amd64. (Fabrice Buoro, with help from Stephen Dolan, Tom Kelly and Mark Shinwell, review by Xavier Leroy)

  • #11025, #11036: Do not pass -no-pie to the C compiler on musl/arm64 (omni, Kate Deplaix and Antonio Nuno Monteiro, review by Xavier Leroy)

  • #11101, #11109: A recursive type constraint fails on 4.14 (Jacques Garrigue, report and review by Florian Angeletti)

  • #11118: Fix integer overflow on 64-bit Windows when indexing bigarrays (which could lead to a segmentation fault). (Roven Gabriel, review by Nicolás Ojeda Bär and Xavier Leroy)