?build.sh: incremental builds (reuse objects),

	unless called as `./build.sh [--clean || --rebuild]` (or unless source code is more new).
	This reduces average build times an order of magnitude,
	but was too much bloat with list of sources to build (thus replaced lists with loops).
	Is progress to issue #18 (which is almost all about build scripts).
	Is followup to: 35b2387 (?`build.sh`: +`OBJDIR`(+`obj/`), +`BINDIR`(+`bin/`)).
	TODO: since generic code replaced most of this, move the generic code into `./Macros.sh` (or other script suitable to reuse).
	TODO: remove `[` clutter, remove `basename` clutter (`> /dev/null` doesn't fix this).

?`README.md`:
	Misc typo fixes.
	?`Console flags:`: How to put `--clean` (or `--rebuild`) to use.
	?`Files:`: Point out that incremental builds require prefix "Class" for local includes.
	Is followup to 58f4a78 (?`README.md`: ... Fixups: ...).

README.md

@@ -22,10 +22,12 @@ Targets: Windows/Linux/Android/OSX/iOS; minimum [_C++11_](https://gcc.gnu.org/pr
 Usage: [`./build.sh [OPTIONS]`](https://github.com/SwuduSusuwu/SubStack/blob/trunk/build.sh) produces objects (`./obj/*.o`, for distribution into other tools,) plus [_Executable and Linkable Format_](https://wikipedia.org/wiki/Executable_and_Linkable_Format) (`./bin/a.out`, to do examples/[unit tests](https://wikipedia.org/wiki/Unit_test#Agile) which prove how effective functions execute,) both of which you can redirect with `export OBJDIR=___` (or `export BINDIR=___`.)
 - [`./cxx/main.hxx`](https://github.com/SwuduSusuwu/SubStack/blob/trunk/cxx/main.hxx) has constants to use to interpret `a.out`'s return values.
 - Console flags:
-  - `./build.sh` : Defaults to `./build.sh --debug`.
+  - `./build.sh` : Defaults to `./build.sh --debug`. For all source code, if intermediate object doesn't exist or is older than source, builds source.
+  - `./build.sh --clean` : removes intermediate object files + exits; to reduce disc use.
+  - `./build.sh --rebuild` : removes intermediate object files + continues; to rebuild with new flags (or if `./build.sh` doesn't rebuild code which includes updated headers).
   - `./build.sh --debug` : includes frame-pointers/debug symbols (`-g`), includes `valgrind`-replacement tools (such as `-fsanitize=address`), optimizes with `-Og`.
   - `./build.sh --release` : excludes `--debug` (`-DNDEBUG`), strips frame-pointers/symbols, optimizes with `-O2`.
-  - `./build.sh --mingw` : can mix with `--release` or `--debug`. Produces [_Portable Executable_](https://wikipedia.org/wiki/Portable_Executable) (`./bin/a.exe`), for _Windows_
+  - `./build.sh --mingw` : can mix with `--release` or `--debug`. Produces [_Portable Executable_](https://wikipedia.org/wiki/Portable_Executable) (`./bin/a.exe`), for _Windows_.
 - Special flags (`vim build.sh` to use); other than `_PREFER_`/`_SKIP_`, most use more resources if set to `true`:
   - Custom `sh` (console) output:
     - `-DSUSUWU_SH_PREFER_STDIO` to replace `std::cXXX << ...` with `fprintf(stdXXX, ...)`; default is `!defined(__cplusplus)`.
@@ -47,28 +49,28 @@ Usage: [`./build.sh [OPTIONS]`](https://github.com/SwuduSusuwu/SubStack/blob/tru
 # Contributor conventions/rules
 Linter: `clang-tidy cxx/*.cxx` /* uses [`.clang-tidy`](https://github.com/SwuduSusuwu/SubStack/blob/trunk/.clang-tidy) options */ 
 ## Git
-Do atomic commits: Commits should allow to use `git rebase -i` to reorder, unless commit messages include such as "Is followup to \<commit hash\>" (which shows temporal order).
+Do atomic commits: if you cannot `./build.sh` your commit if it is swapped (such as through `git rebase -i`) with a previous commit, or cannot `./build.sh` if a previous commit got `git revert`, your commit message must include such as "Is followup to \<commit hash\>" (which shows temporal order).
 
 `git commit` message format/syntax:
-- if commit does `git add NewFile`: message has `+\`NewFile\``
-- if `git rm Exists`: `-`Exists``
-- if `touch Exists && git add Exists`: `@\`Exists\`` or `?\`Exists\``
-  - Simple wildcards/regex for altered functions: `\`%s/oldFunction/newFunction/\``
+- if commit does `git add NewFile`: message has `+\`NewFile\``.
+- if `git rm Exists`: `-`Exists``.
+- if `touch Exists && git add Exists`: `@\`Exists\`` or `?\`Exists\``.
+  - Simple wildcards/regex for altered functions: `\`%s/oldFunction/newFunction/\``.
 - if `echo "int newFunction() {...}" >> Exists && git add Exists`: `@\`Exists\`:+\`NewFunction()\``.
-- if `git mv OldPath/ NewPath/`: `\`OldPath/.* -> NewPath/.*\``
+- if `git mv OldPath/ NewPath/`: `\`OldPath/.* -> NewPath/.*\``.
 
 [Notice: Commit titles can omit backticks (``) if not enough room; the backticks just allow _GitHub_ to format code/paths.]
 ## Source
 Most of what [_Mozilla Org_'s (_Firefox_'s) style](https://firefox-source-docs.mozilla.org/code-quality/coding-style/coding_style_cpp.html) suggests is sound (you should follow this unless you have specific reasons not to).
 Code rules (lots overlap with _Mozilla Org_'s):
 
-- Files: `#import "PascalCase.hxx"`, as this is most common.
+- Files: `#include "PascalCase.hxx"`, as this is most common. `./build.sh` requires: that all local includes prefix as `Class*.hxx` (so it knows to execute `--rebuild` if you upgrade a common include.) TODO: incremental builds which don't require this.
 
 - Structs, enums, classe: `typedef struct PascalCase {} PascalCase;`, `typedef enum PascalCase {} PascalCase;`, `typedef class PascalCase {} PascalCase;`, as this is most common.
 
 - Macros: `#define NAMESPACE_CONSTANT_CASE(snake_case_param) assert(snake_case_param);`, as this is most common.
 
-- Indent: tabs ('^I', reduced memory use, allows local configs to set width, allows arrow keys to move fast); as much tabs as braces ('{', '}'). [All which conflicts with _Mozilla Org_'s format is tab use]
+- Indent: tabs ('^I', reduced memory use, allows local configs to set width, allows arrow keys to move fast); as much tabs as braces ('{', '}'). [All which conflicts with _Mozilla Org_'s format is tab use.]
 
 - Braces, functions; most common form:
 ```
@@ -106,7 +108,7 @@ const /* const prevents `if(func() = x)` where you wished for `if(func() == x)`
 bool functionDeclaration(std::string input, std::deque<vector> output);
 ```
   - It is arguable whether or not you should document such possible system errors; almost all Standard Template Library functions can throw derivatives of `std::logic_error`.
-  - Regex `:%s/@pre (.*) @code (.*) @endcode/[[expects: \2]] \\* \1 \\*/` `:%s/@post (.*) @code (.*) @endcode/[[ensures: \2]] \\* \1 \\*/` once have _Contracts_/_C++26_
+  - Regex `:%s/@pre (.*) @code (.*) @endcode/[[expects: \2]] \\* \1 \\*/` `:%s/@post (.*) @code (.*) @endcode/[[ensures: \2]] \\* \1 \\*/` once have _Contracts_/_C++26_.
   - cxx/Macros.cxx has `ASSUME(X)`, which is close to `[[expects: x]]`, but `ASSUME(X)` goes to `*.cxx`, whereas `[[expects]]` goes to `*.hxx`.
   - Documentation of interfaces belongs to `*.hxx`; `*.cxx` is to do implementations. Do not duplicate interface comments.
   - Advantages of `[[expects]]`; allows to move information of interfaces out of `*.cxx`, to `*.hxx`.

build.sh

@@ -15,7 +15,7 @@ CXXFLAGS_FSAN="-fsanitize=address -fno-sanitize-recover=all -fsanitize=float-div
 #CXXFLAGS_FSAN="${CXXFLAGS_FSAN} -fsanitize=undefined" #/* causes 'cannot locate symbol "__ubsan_handle_function_type_mismatch_abort"' */
 
 CROSS_COMP=""
-if [ "--mingw" = "${1}" ] || [ "--mingw" = "${2}" ]; then
+if [ "--mingw" = "${1}" -o  "--mingw" = "${2}" ]; then
 	CROSS_COMP=" --mingw"
 	LDFLAGS="${LDFLAGS} -static-libgcc -static-libstdc++"
 	if command -v x86_64-w64-mingw32-clang++ > /dev/null; then
@@ -41,7 +41,7 @@ else
 	exit 1
 fi
 
-if [ "--release" = "${1}" ] || [ "--release" = "${2}" ]; then
+if [ "--release" = "${1}" -o  "--release" = "${2}" ]; then
 	SUSUWU_PRINT "${SUSUWU_SH_NOTICE}" "\`${0}${CROSS_COMP} --release\` does not support profilers/debuggers (use \`${0}${CROSS_COMP} --debug\` for this)."
 	CXXFLAGS="${CXXFLAGS} ${CXXFLAGS_RELEASE}"
 else
@@ -79,30 +79,62 @@ else
 	SUSUWU_PRINT "${SUSUWU_SH_NOTICE}" "\`${LD} ... -o \${BINDIR}${OUTPUT}\` inherits local \`BINDIR=\"${BINDIR}\"\` until you execute \`unset BINDIR\`."
 fi
 mkdir -p "${OBJDIR}" "${BINDIR}"
+if [ "--rebuild" = "${1}" -o  "--rebuild" = "${2}" ]; then
+	SUSUWU_PRINT "${SUSUWU_SH_NOTICE}" "Was called with \`${0}${CROSS_COMP} --rebuild\`, will remove intermediate objects+ continue."
+	rm ${OBJDIR}*.o
+fi
+if [ "--clean" = "${1}" -o  "--clean" = "${2}" ]; then
+	SUSUWU_PRINT "${SUSUWU_SH_NOTICE}" "Was called with \`${0}${CROSS_COMP} --clean\`, will remove intermediate objects + exit. Use \`${0}${CROSS_COMP} --rebuild\` to clean + continue."
+	rm ${OBJDIR}*.o
+	exit 0
+fi
 
 C_SOURCE_PATH=$(SUSUWU_DIR_SUFFIX_SLASH "${C_SOURCE_PATH}") #/* if inherit C_SOURCE_PATH, perhaps it lacks '/' */
 CXX_SOURCE_PATH=$(SUSUWU_DIR_SUFFIX_SLASH "${CXX_SOURCE_PATH}") #/* if inherit CXX_SOURCE_PATH, perhaps it lacks '/' */
 OBJDIR=$(SUSUWU_DIR_SUFFIX_SLASH "${OBJDIR}") #/* if inherit OBJDIR, perhaps it is without last '/' */
 BINDIR=$(SUSUWU_DIR_SUFFIX_SLASH "${BINDIR}") #/* if inherit BINDIR, perhaps it is without last '/' */
+if [ -e ${BINDIR}${OUTPUT} ]; then
+	BUILDNEW=false
+else
+	BUILDNEW=true
+fi
+for SOURCE in ${CXX_SOURCE_PATH}Class*.hxx ${CXX_SOURCE_PATH}Macros.hxx; do
+	OBJECT="${OBJDIR}$(basename ${SOURCE} .hxx).o" #/* `basename`'s second param removes suffix */
+	SRCCXX="${CXX_SOURCE_PATH}$(basename ${SOURCE} .hxx).cxx" #/* `basename`'s second param removes suffix */
+	if [ ${OBJECT} -ot ${SOURCE} -a -e ${SOURCE} ]; then #/* `&& [ -e ${SOURCE} ]` is: skip unless `${SOURCE}` exists. */
+		SUSUWU_PRINT "${SUSUWU_SH_NOTICE}" "\`${SOURCE}\` is newer than \`${OBJECT}\`, will rebuild all objects."
+		rm ${OBJDIR}*.o
+		break
+	elif [ ! -e ${SRCCXX} ]; then #/* If `*.hxx` doesn't have `*.cxx` match,     */
+		touch ${OBJECT};            #/* ... then produce `*.o` (for future tests.) */
+	fi
+done
+OBJECTLIST=""
 set -x
-${CC} ${CCFLAGS} -c "${C_SOURCE_PATH}rfc6234/sha1.c" -o "${OBJDIR}sha1.o"
-${CC} ${CCFLAGS} -c "${C_SOURCE_PATH}rfc6234/sha224-256.c" -o "${OBJDIR}sha224-256.o"
-${CC} ${CCFLAGS} -c "${C_SOURCE_PATH}rfc6234/sha384-512.c" -o "${OBJDIR}sha384-512.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}Macros.cxx" -o "${OBJDIR}Macros.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}ClassSha2.cxx" -o "${OBJDIR}ClassSha2.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}ClassResultList.cxx" -o "${OBJDIR}ClassResultList.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}ClassSys.cxx" -o "${OBJDIR}ClassSys.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}ClassCns.cxx" -o "${OBJDIR}ClassCns.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}VirusAnalysis.cxx" -o "${OBJDIR}VirusAnalysis.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}AssistantCns.cxx" -o "${OBJDIR}AssistantCns.o"
-${CXX} ${CXXFLAGS} -c "${CXX_SOURCE_PATH}main.cxx" -o "${OBJDIR}main.o"
-#/* Order is 2 fold: language of code, plus which source the most `#include` (most include `Macros.hxx`). */
-${LD} ${LDFLAGS} "${OBJDIR}sha1.o" "${OBJDIR}sha224-256.o" "${OBJDIR}sha384-512.o" "${OBJDIR}Macros.o" "${OBJDIR}ClassSha2.o" "${OBJDIR}ClassResultList.o" "${OBJDIR}ClassSys.o" "${OBJDIR}ClassCns.o" "${OBJDIR}VirusAnalysis.o" "${OBJDIR}AssistantCns.o" "${OBJDIR}main.o" -o "${BINDIR}${OUTPUT}"
+#for SOURCE in ${C_SOURCE_PATH}*/*.c; do #/* The extra "*/" is since this just has vendored code (`rfc6234/`) */
+for SOURCE in "${C_SOURCE_PATH}rfc6234/sha1.c" "${C_SOURCE_PATH}rfc6234/sha224-256.c" "${C_SOURCE_PATH}rfc6234/sha384-512.c"; do
+	OBJECT="${OBJDIR}$(basename ${SOURCE} .c).o" #/* `basename`'s second param removes suffix */
+	if [ ${OBJECT} -ot ${SOURCE} -o ! -e ${OBJECT} ] >/dev/null; then
+		${CC} ${CCFLAGS} -c "${SOURCE}" -o "${OBJECT}"
+		BUILDNEW=true
+	fi
+	OBJECTLIST="${OBJECTLIST} ${OBJECT}"
+done
+for SOURCE in ${CXX_SOURCE_PATH}*.cxx; do
+	OBJECT="${OBJDIR}$(basename ${SOURCE} .cxx).o" #/* `basename`'s second param removes suffix */
+	if [ ${OBJECT} -ot ${SOURCE} -o ! -e ${OBJECT} ] > /dev/null 2>&1; then
+		${CXX} ${CXXFLAGS} -c "${SOURCE}" -o "${OBJECT}"
+		BUILDNEW=true
+	fi
+	OBJECTLIST="${OBJECTLIST} ${OBJECT}"
+done
+${BUILDNEW} && ${LD} ${LDFLAGS}${OBJECTLIST} -o "${BINDIR}${OUTPUT}"
 STATUS=$?
 set +x
 
-if [ 0 -eq ${STATUS} ]; then
-	SUSUWU_PRINT "${SUSUWU_SH_SUCCESS}" "produced \`${BINDIR}${OUTPUT}\` (`stat -c%s ${BINDIR}${OUTPUT}` bytes)."
+if [ 0 -eq ${STATUS} -o false = ${BUILDNEW} ]; then
+	${BUILDNEW} && SUSUWU_PRINT "${SUSUWU_SH_SUCCESS}" "produced \`${BINDIR}${OUTPUT}\` (`stat -c%s ${BINDIR}${OUTPUT}` bytes)."
+	${BUILDNEW} || SUSUWU_PRINT "${SUSUWU_SH_SUCCESS}" "reused \`${BINDIR}${OUTPUT}\` (`stat -c%s ${BINDIR}${OUTPUT}` bytes)."
 	BINDIR=$(SUSUWU_DIR_AFFIX_DOTSLASH "${BINDIR}")
 	${BINDIR}${OUTPUT}
 	STATUS=$?