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])])])