X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/e5b61a8dec3586f96d25bd3ef454176526ff0f69..1c3d4cf54a0edd484c4405f5332d39bb17f1aee0:/m4/mdw-probe-constant.m4 diff --git a/m4/mdw-probe-constant.m4 b/m4/mdw-probe-constant.m4 new file mode 100644 index 00000000..39165820 --- /dev/null +++ b/m4/mdw-probe-constant.m4 @@ -0,0 +1,183 @@ +dnl -*-autoconf-*- + +### SYNOPSIS +### +### mdw_PROBE_CONSTANT(VAR, EXPR, [PREAMBLE], [IF-FAILED]) +### +### DESCRIPTION +### +### Extracts the value of a a constant integer expression from the +### compiler. This works even if the compiler in question doesn't target +### the current architecture. The value must be in the range -10^244 < x < +### 10^244; this is probably fair enough. In the extraordinarily unliklely +### event that the constant value is outside these bounds, the macro will +### fail rather than silently giving a wrong answer. +### +### The result of the macro is that the shell variable VAR has the value of +### the expression EXPR, in decimal. The PREAMBLE, if given, is inserted +### before EXPR is evaluated; it should contain #include and #define +### directives which are used to compute the value of the expression. +### +### The idea for this macro came from the AC_C_COMPILE_VALUE macro by +### Ilguiz Latypov; this implementation has a number of advantages: +### +### * it has an immense range of representable values, notably including +### negative numbers; and +### +### * it returns the value directly in a shell variable rather than +### inventing an AC_DEFINE for it. +### +### LICENSE +### +### Copyright (c) 2013 Mark Wooding +### +### This program is free software: you can redistribute it and/or modify it +### under the terms of the GNU General Public License as published by the +### Free Software Foundation, either version 2 of the License, or (at your +### option) any later version. +### +### This program is distributed in the hope that it will be useful, but +### WITHOUT ANY WARRANTY; without even the implied warranty of +### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +### General Public License for more details. +### +### You should have received a copy of the GNU General Public License along +### with this program. If not, see . +### +### In particular, no exception to the GPL is granted regarding generated +### `configure' scripts which are the output of Autoconf. + +# Serial 1 +AC_COPYRIGHT([ +Portions copyright (c) 2013 Mark Wooding. + +This configure script is free software: you can redistribute it and/or +modify it under he terms of the GNU General Public License as published +by the Free Software Foundation, either version 2 of the License, or +(at your option) any later version.]) + +AC_DEFUN([mdw__PROBE_CONSTANT_SETUP], + [mdw__probe_constant_body="[ + +/* The following program is copyright (c) 2013 Mark Wooding. It is free + * software: you can redistribute it and/or modify it under the terms of the + * GNU General Public License as published by the Free Software Foundation, + * either version 2 of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program. If not, see . + */ + +/* The constant: 1 billion. We'll pull digits out in groups of nine, since + * we can work with constants of at least the size of a C \`long'. + */ +#define MDW__G 1000000000 + +/* An empty macro, used as an argument sometimes. */ +#define MDW__E + +/* A cheesy compile-time assertion. If X is zero, then we try to declare + * an array with a negative number of elements. Wrap this up in an anonymous + * struct so that we don't have to worry about naming things if we make + * more than one assertion. + */ +#define MDW__ASSERT(x) struct { int v[1 - 2*!(x)]; } + +/* Return the value of X/DIV, with further divisions D applied, truncating + * towards zero. DIV must be greater than one. This works even if X is + * negative, never tries to divide negative numbers, and doesn't try to + * negate the most-negative value. There are three cases: if X <= -DIV then + * X/DIV = -(X + DIV)/DIV - 1, and X + DIV is less negative than X so this is + * a safe negation; if -DIV < X < 0 then the result is zero; otherwise, X + * is nonnegative so the straightforward division is safe. Because DIV > 1, + * X/DIV is safe to negate, and we can apply the remaining divisions to it. + */ +#define MDW__SHIFT(x, div, d) \\ + ((x) >= 0 ? ((x)/div d) : \\ + (x) <= -(div) ? -((-((x) + (div))/(div) + 1) d) : 0) + +/* Extract the bottommost digit of X, as an integer: i.e., the value of + * abs(X) mod 10. This works even if X is negative, never tries to divide + * negative numbers, and doesn't try to divide the most-negative value. + */ +#define MDW__RAW_DIGIT(x) (((x) < 0 ? -((x) + 1) % 10 + 1 : (x)) % 10) + +/* Extract the bottommost digit of X, as a character; if X is zero, then + * produce a space instead. This avoids leading zeroes which can be + * misinterpreted by callers. + */ +#define MDW__TEXT_DIGIT(x) ((x) ? '0' + MDW__RAW_DIGIT(x) : ' ') + +/* Extract the bottommost digit of the probe value, after dividing by DIV + * and applying the divisons D. + */ +#define MDW__DIGIT(div, d) \\ + MDW__TEXT_DIGIT(MDW__SHIFT(MDW__PROBE_EXPR, div, d)) + +/* Extract the bottommost six digits of the probe value after dividing by 10 + * and then applying the divisions D. + */ +#define MDW__9DIGITS(d) \\ + MDW__DIGIT(1000000000, d), \\ + MDW__DIGIT( 100000000, d), \\ + MDW__DIGIT( 10000000, d), \\ + MDW__DIGIT( 1000000, d), \\ + MDW__DIGIT( 100000, d), \\ + MDW__DIGIT( 10000, d), \\ + MDW__DIGIT( 1000, d), \\ + MDW__DIGIT( 100, d), \\ + MDW__DIGIT( 10, d) + +/* Increasingly huge divisions. PN divides by 10^(9*2^N). */ +#define MDW__P0 /MDW__G +#define MDW__P1 MDW__P0 MDW__P0 +#define MDW__P2 MDW__P1 MDW__P1 +#define MDW__P3 MDW__P2 MDW__P2 +#define MDW__P4 MDW__P3 MDW__P3 +#define MDW__P5 MDW__P4 MDW__P4 + +/* Increasingly long sequences of digits. DN(P) produces the 9 * 2^N + * digits after applying divisions P. + */ +#define MDW__D0(p) MDW__9DIGITS(p MDW__P0), MDW__9DIGITS(p MDW__E) +#define MDW__D1(p) MDW__D0(p MDW__P1), MDW__D0(p) +#define MDW__D2(p) MDW__D1(p MDW__P2), MDW__D1(p) +#define MDW__D3(p) MDW__D2(p MDW__P3), MDW__D2(p) +#define MDW__D4(p) MDW__D3(p MDW__P4), MDW__D3(p) + +/* Ensure that our exponential cascade is sufficient to represent the + * expression. + */ +MDW__ASSERT(MDW__SHIFT(MDW__PROBE_EXPR, 10, MDW__P5) == 0); + +/* Format the output. Everything is taken care of except the bottommost + * digit, which we handle seaprately because we actually want a \`leading' + * zero here if the constant value is actually zero. Format it so that + * we can extract it from the object file. + */ +const char mdw__probe_output[] = { + '\\n', + 'm', 'd', 'w', '-', + 'p', 'r', 'o', 'b', 'e', '-', + 'v', 'a', 'l', 'u', 'e', '=', '\"', + (MDW__PROBE_EXPR < 0 ? '-' : ' '), + MDW__D4(MDW__E), + '0' + MDW__RAW_DIGIT(MDW__PROBE_EXPR), + '\"', '\\n' +};]"]) + +AC_DEFUN([mdw_PROBE_CONSTANT], + [AC_REQUIRE([mdw__PROBE_CONSTANT_SETUP]) + AC_COMPILE_IFELSE([AC_LANG_SOURCE([[$3 +#define MDW__PROBE_EXPR ($2) +$mdw__probe_constant_body]])], + [$1=$(sed -n \ + 's:^mdw-probe-value="\(-\|\) *\([[0-9]]*\)"$:\1\2:p' conftest.o)], + [m4_if([$4], [], + [AC_MSG_FAILURE([failed to evaluate expression])], + [$4])])])