Re: [PATCH v3] replace timeconst bc script with an sh script

[hpa@zytor.com]

On October 29, 2019 2:02:44 PM PDT, Ethan Sommer <e5ten.arch@gmail.com> wrote:
>removes the bc build dependency introduced when timeconst.pl was
>replaced by timeconst.bc:
>commit 70730bca1331 ("kernel: Replace timeconst.pl with a bc script")
>
>the reason for this change is that this is the only use of bc in the
>actual compilation of the kernel, so by replacing it with a shell
>script
>compiling the kernel no longer depends on bc.
>
>Signed-off-by: Ethan Sommer <e5ten.arch@gmail.com>
>---
> Documentation/process/changes.rst |   6 --
> Kbuild                            |   4 +-
> kernel/time/timeconst.bc          | 117 ------------------------------
> kernel/time/timeconst.sh          | 111 ++++++++++++++++++++++++++++
> 4 files changed, 113 insertions(+), 125 deletions(-)
> delete mode 100644 kernel/time/timeconst.bc
> create mode 100644 kernel/time/timeconst.sh
>
>diff --git a/Documentation/process/changes.rst
>b/Documentation/process/changes.rst
>index 2284f2221f02..3ae168387109 100644
>--- a/Documentation/process/changes.rst
>+++ b/Documentation/process/changes.rst
>@@ -105,12 +105,6 @@ Perl
> You will need perl 5 and the following modules: ``Getopt::Long``,
>``Getopt::Std``, ``File::Basename``, and ``File::Find`` to build the
>kernel.
> 
>-BC
>---
>-
>-You will need bc to build kernels 3.10 and higher
>-
>-
> OpenSSL
> -------
> 
>diff --git a/Kbuild b/Kbuild
>index 3109ac786e76..7eba24cbdb78 100644
>--- a/Kbuild
>+++ b/Kbuild
>@@ -18,9 +18,9 @@ $(bounds-file): kernel/bounds.s FORCE
> 
> timeconst-file := include/generated/timeconst.h
> 
>-filechk_gentimeconst = echo $(CONFIG_HZ) | bc -q $<
>+filechk_gentimeconst = $(CONFIG_SHELL) $< $(CONFIG_HZ)
> 
>-$(timeconst-file): kernel/time/timeconst.bc FORCE
>+$(timeconst-file): kernel/time/timeconst.sh FORCE
> 	$(call filechk,gentimeconst)
> 
> #####
>diff --git a/kernel/time/timeconst.bc b/kernel/time/timeconst.bc
>deleted file mode 100644
>index 7ed0e0fb5831..000000000000
>--- a/kernel/time/timeconst.bc
>+++ /dev/null
>@@ -1,117 +0,0 @@
>-/* SPDX-License-Identifier: GPL-2.0 */
>-
>-scale=0
>-
>-define gcd(a,b) {
>-	auto t;
>-	while (b) {
>-		t = b;
>-		b = a % b;
>-		a = t;
>-	}
>-	return a;
>-}
>-
>-/* Division by reciprocal multiplication. */
>-define fmul(b,n,d) {
>-       return (2^b*n+d-1)/d;
>-}
>-
>-/* Adjustment factor when a ceiling value is used.  Use as:
>-   (imul * n) + (fmulxx * n + fadjxx) >> xx) */
>-define fadj(b,n,d) {
>-	auto v;
>-	d = d/gcd(n,d);
>-	v = 2^b*(d-1)/d;
>-	return v;
>-}
>-
>-/* Compute the appropriate mul/adj values as well as a shift count,
>-   which brings the mul value into the range 2^b-1 <= x < 2^b.  Such
>-   a shift value will be correct in the signed integer range and off
>-   by at most one in the upper half of the unsigned range. */
>-define fmuls(b,n,d) {
>-	auto s, m;
>-	for (s = 0; 1; s++) {
>-		m = fmul(s,n,d);
>-		if (m >= 2^(b-1))
>-			return s;
>-	}
>-	return 0;
>-}
>-
>-define timeconst(hz) {
>-	print "/* Automatically generated by kernel/time/timeconst.bc */\n"
>-	print "/* Time conversion constants for HZ == ", hz, " */\n"
>-	print "\n"
>-
>-	print "#ifndef KERNEL_TIMECONST_H\n"
>-	print "#define KERNEL_TIMECONST_H\n\n"
>-
>-	print "#include <linux/param.h>\n"
>-	print "#include <linux/types.h>\n\n"
>-
>-	print "#if HZ != ", hz, "\n"
>-	print "#error \qinclude/generated/timeconst.h has the wrong HZ
>value!\q\n"
>-	print "#endif\n\n"
>-
>-	if (hz < 2) {
>-		print "#error Totally bogus HZ value!\n"
>-	} else {
>-		s=fmuls(32,1000,hz)
>-		obase=16
>-		print "#define HZ_TO_MSEC_MUL32\tU64_C(0x", fmul(s,1000,hz), ")\n"
>-		print "#define HZ_TO_MSEC_ADJ32\tU64_C(0x", fadj(s,1000,hz), ")\n"
>-		obase=10
>-		print "#define HZ_TO_MSEC_SHR32\t", s, "\n"
>-
>-		s=fmuls(32,hz,1000)
>-		obase=16
>-		print "#define MSEC_TO_HZ_MUL32\tU64_C(0x", fmul(s,hz,1000), ")\n"
>-		print "#define MSEC_TO_HZ_ADJ32\tU64_C(0x", fadj(s,hz,1000), ")\n"
>-		obase=10
>-		print "#define MSEC_TO_HZ_SHR32\t", s, "\n"
>-
>-		obase=10
>-		cd=gcd(hz,1000)
>-		print "#define HZ_TO_MSEC_NUM\t\t", 1000/cd, "\n"
>-		print "#define HZ_TO_MSEC_DEN\t\t", hz/cd, "\n"
>-		print "#define MSEC_TO_HZ_NUM\t\t", hz/cd, "\n"
>-		print "#define MSEC_TO_HZ_DEN\t\t", 1000/cd, "\n"
>-		print "\n"
>-
>-		s=fmuls(32,1000000,hz)
>-		obase=16
>-		print "#define HZ_TO_USEC_MUL32\tU64_C(0x", fmul(s,1000000,hz),
>")\n"
>-		print "#define HZ_TO_USEC_ADJ32\tU64_C(0x", fadj(s,1000000,hz),
>")\n"
>-		obase=10
>-		print "#define HZ_TO_USEC_SHR32\t", s, "\n"
>-
>-		s=fmuls(32,hz,1000000)
>-		obase=16
>-		print "#define USEC_TO_HZ_MUL32\tU64_C(0x", fmul(s,hz,1000000),
>")\n"
>-		print "#define USEC_TO_HZ_ADJ32\tU64_C(0x", fadj(s,hz,1000000),
>")\n"
>-		obase=10
>-		print "#define USEC_TO_HZ_SHR32\t", s, "\n"
>-
>-		obase=10
>-		cd=gcd(hz,1000000)
>-		print "#define HZ_TO_USEC_NUM\t\t", 1000000/cd, "\n"
>-		print "#define HZ_TO_USEC_DEN\t\t", hz/cd, "\n"
>-		print "#define USEC_TO_HZ_NUM\t\t", hz/cd, "\n"
>-		print "#define USEC_TO_HZ_DEN\t\t", 1000000/cd, "\n"
>-
>-		cd=gcd(hz,1000000000)
>-		print "#define HZ_TO_NSEC_NUM\t\t", 1000000000/cd, "\n"
>-		print "#define HZ_TO_NSEC_DEN\t\t", hz/cd, "\n"
>-		print "#define NSEC_TO_HZ_NUM\t\t", hz/cd, "\n"
>-		print "#define NSEC_TO_HZ_DEN\t\t", 1000000000/cd, "\n"
>-		print "\n"
>-
>-		print "#endif /* KERNEL_TIMECONST_H */\n"
>-	}
>-	halt
>-}
>-
>-hz = read();
>-timeconst(hz)
>diff --git a/kernel/time/timeconst.sh b/kernel/time/timeconst.sh
>new file mode 100644
>index 000000000000..d1aa25f46be8
>--- /dev/null
>+++ b/kernel/time/timeconst.sh
>@@ -0,0 +1,111 @@
>+#!/bin/sh
>+# SPDX-License-Identifier: GPL-2.0
>+
>+if [ -z "$1" ]; then
>+	printf '%s <HZ>\n' "$0" >&2
>+	exit 1
>+fi
>+
>+# 2 to the power of n
>+pot() {
>+	local i=1 j=0
>+	while [ "$((j += 1))" -le "$1" ]; do
>+		: "$((i *= 2))"
>+	done
>+	printf '%u' "${i}"
>+}
>+
>+# Greatest common denominator
>+gcd() {
>+	local i="$1" j="$2" k
>+	while [ "${j}" -ne 0 ]; do
>+		k="${j}" j="$((i % j))" i="${k}"
>+	done
>+	printf '%u' "${i}"
>+}
>+
>+# Division by reciprocal multiplication.
>+fmul() {
>+	printf '%u' "$((($(pot "$1") * $2 + $3 - 1) / $3))"
>+}
>+
>+# Adjustment factor when a ceiling value is used.
>+fadj() {
>+	local i
>+	i="$(gcd "$2" "$3")"
>+	printf '%u' "$(($(pot "$1") * ($3 / i - 1) / ($3 / i)))"
>+}
>+
>+# Compute the appropriate mul/adj values as well as a shift count,
>+# which brings the mul value into the range 2^b-1 <= x < 2^b.  Such
>+# a shift value will be correct in the signed integer range and off
>+# by at most one in the upper half of the unsigned range.
>+fmuls() {
>+	local i=0 j
>+	while true; do
>+		j="$(fmul "${i}" "$2" "$3")"
>+		if [ "${j}" -ge "$(pot "$(($1 - 1))")" ]; then
>+			printf '%u' "${i}"
>+			return
>+		fi
>+		: "$((i += 1))"
>+	done
>+}
>+
>+printf '/* Automatically generated by kernel/time/timeconst.sh */\n'
>+printf '/* Time conversion constants for HZ == %u */\n\n' "$1"
>+
>+printf '#ifndef KERNEL_TIMECONST_H\n'
>+printf '#define KERNEL_TIMECONST_H\n\n'
>+
>+printf '#include <linux/param.h>\n'
>+printf '#include <linux/types.h>\n\n'
>+
>+printf '#if HZ != %u\n' "$1"
>+printf '#error "include/generated/timeconst.h has the wrong HZ
>value!"\n'
>+printf '#endif\n\n'
>+
>+if [ "$1" -lt 2 ]; then
>+	printf '#error Totally bogus HZ value!\n'
>+	exit 1
>+fi
>+
>+s="$(fmuls 32 1000 "$1")"
>+printf '#define HZ_TO_MSEC_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" 1000
>"$1")"
>+printf '#define HZ_TO_MSEC_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" 1000
>"$1")"
>+printf '#define HZ_TO_MSEC_SHR32\t%u\n' "${s}"
>+
>+s="$(fmuls 32 "$1" 1000)"
>+printf '#define MSEC_TO_HZ_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" "$1"
>1000)"
>+printf '#define MSEC_TO_HZ_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" "$1"
>1000)"
>+printf '#define MSEC_TO_HZ_SHR32\t%u\n' "${s}"
>+
>+cd="$(gcd "$1" 1000)"
>+printf '#define HZ_TO_MSEC_NUM\t\t%u\n' "$((1000 / cd))"
>+printf '#define HZ_TO_MSEC_DEN\t\t%u\n' "$(($1 / cd))"
>+printf '#define MSEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
>+printf '#define MSEC_TO_HZ_DEN\t\t%u\n\n' "$((1000 / cd))"
>+
>+s="$(fmuls 32 1000000 "$1")"
>+printf '#define HZ_TO_USEC_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}"
>1000000 "$1")"
>+printf '#define HZ_TO_USEC_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}"
>1000000 "$1")"
>+printf '#define HZ_TO_USEC_SHR32\t%u\n' "${s}"
>+
>+s="$(fmuls 32 "$1" 1000000)"
>+printf '#define USEC_TO_HZ_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" "$1"
>1000000)"
>+printf '#define USEC_TO_HZ_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" "$1"
>1000000)"
>+printf '#define USEC_TO_HZ_SHR32\t%u\n' "${s}"
>+
>+cd="$(gcd "$1" 1000000)"
>+printf '#define HZ_TO_USEC_NUM\t\t%u\n' "$((1000000 / cd))"
>+printf '#define HZ_TO_USEC_DEN\t\t%u\n' "$(($1 / cd))"
>+printf '#define USEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
>+printf '#define USEC_TO_HZ_DEN\t\t%u\n' "$((1000000 / cd))"
>+
>+cd="$(gcd "$1" 1000000000)"
>+printf '#define HZ_TO_NSEC_NUM\t\t%u\n' "$((1000000000 / cd))"
>+printf '#define HZ_TO_NSEC_DEN\t\t%u\n' "$(($1 / cd))"
>+printf '#define NSEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
>+printf '#define NSEC_TO_HZ_DEN\t\t%u\n' "$((1000000000 / cd))"
>+
>+printf '\n#endif /* KERNEL_TIMECONST_H */\n'

Please let me point out, again, that bc *is* part of the basic POSIX toolset, and the only tool in that toolset that allows for arbitrary-precision arithmetic. That being said, GNU as, which we also depends on, also contains bigint arithmetic, so it might be possible to coax as into outputting ASCII output without manually implementing bigints manually.

Another option would be to use a C program linked with gmp. Binutils requires gmp, so it doesn't inherently add dependencies, but running it though as would probably be easier at least for the LLVM guys.

I also have written a small, portable C bigint library, but that is a lot of code to add to the tree.
-- 
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