| 1 | dnl -*-autoconf-*- |
| 2 | |
| 3 | ### SYNOPSIS |
| 4 | ### |
| 5 | ### mdw_PROBE_CONSTANT(VAR, EXPR, [PREAMBLE], [IF-FAILED]) |
| 6 | ### |
| 7 | ### DESCRIPTION |
| 8 | ### |
| 9 | ### Extracts the value of a a constant integer expression from the |
| 10 | ### compiler. This works even if the compiler in question doesn't target |
| 11 | ### the current architecture. The value must be in the range -10^244 < x < |
| 12 | ### 10^244; this is probably fair enough. In the extraordinarily unliklely |
| 13 | ### event that the constant value is outside these bounds, the macro will |
| 14 | ### fail rather than silently giving a wrong answer. |
| 15 | ### |
| 16 | ### The result of the macro is that the shell variable VAR has the value of |
| 17 | ### the expression EXPR, in decimal. The PREAMBLE, if given, is inserted |
| 18 | ### before EXPR is evaluated; it should contain #include and #define |
| 19 | ### directives which are used to compute the value of the expression. |
| 20 | ### |
| 21 | ### The idea for this macro came from the AC_C_COMPILE_VALUE macro by |
| 22 | ### Ilguiz Latypov; this implementation has a number of advantages: |
| 23 | ### |
| 24 | ### * it has an immense range of representable values, notably including |
| 25 | ### negative numbers; and |
| 26 | ### |
| 27 | ### * it returns the value directly in a shell variable rather than |
| 28 | ### inventing an AC_DEFINE for it. |
| 29 | ### |
| 30 | ### LICENSE |
| 31 | ### |
| 32 | ### Copyright (c) 2013 Mark Wooding <mdw@distorted.org.uk> |
| 33 | ### |
| 34 | ### This program is free software: you can redistribute it and/or modify it |
| 35 | ### under the terms of the GNU General Public License as published by the |
| 36 | ### Free Software Foundation, either version 2 of the License, or (at your |
| 37 | ### option) any later version. |
| 38 | ### |
| 39 | ### This program is distributed in the hope that it will be useful, but |
| 40 | ### WITHOUT ANY WARRANTY; without even the implied warranty of |
| 41 | ### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 42 | ### General Public License for more details. |
| 43 | ### |
| 44 | ### You should have received a copy of the GNU General Public License along |
| 45 | ### with this program. If not, see <http://www.gnu.org/licenses/>. |
| 46 | ### |
| 47 | ### In particular, no exception to the GPL is granted regarding generated |
| 48 | ### `configure' scripts which are the output of Autoconf. |
| 49 | |
| 50 | # Serial 1 |
| 51 | AC_COPYRIGHT([ |
| 52 | Portions copyright (c) 2013 Mark Wooding. |
| 53 | |
| 54 | This configure script is free software: you can redistribute it and/or |
| 55 | modify it under he terms of the GNU General Public License as published |
| 56 | by the Free Software Foundation, either version 2 of the License, or |
| 57 | (at your option) any later version.]) |
| 58 | |
| 59 | AC_DEFUN([mdw__PROBE_CONSTANT_SETUP], |
| 60 | [mdw__probe_constant_body="[ |
| 61 | |
| 62 | /* The following program is copyright (c) 2013 Mark Wooding. It is free |
| 63 | * software: you can redistribute it and/or modify it under the terms of the |
| 64 | * GNU General Public License as published by the Free Software Foundation, |
| 65 | * either version 2 of the License, or (at your option) any later version. |
| 66 | * |
| 67 | * This program is distributed in the hope that it will be useful, but |
| 68 | * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 69 | * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 70 | * for more details. |
| 71 | * |
| 72 | * You should have received a copy of the GNU General Public License along |
| 73 | * with this program. If not, see <http://www.gnu.org/licenses/>. |
| 74 | */ |
| 75 | |
| 76 | /* The constant: 1 billion. We'll pull digits out in groups of nine, since |
| 77 | * we can work with constants of at least the size of a C \`long'. |
| 78 | */ |
| 79 | #define MDW__G 1000000000 |
| 80 | |
| 81 | /* An empty macro, used as an argument sometimes. */ |
| 82 | #define MDW__E |
| 83 | |
| 84 | /* A cheesy compile-time assertion. If X is zero, then we try to declare |
| 85 | * an array with a negative number of elements. Wrap this up in an anonymous |
| 86 | * struct so that we don't have to worry about naming things if we make |
| 87 | * more than one assertion. |
| 88 | */ |
| 89 | #define MDW__ASSERT(x) struct { int v[1 - 2*!(x)]; } |
| 90 | |
| 91 | /* Return the value of X/DIV, with further divisions D applied, truncating |
| 92 | * towards zero. DIV must be greater than one. This works even if X is |
| 93 | * negative, never tries to divide negative numbers, and doesn't try to |
| 94 | * negate the most-negative value. There are three cases: if X <= -DIV then |
| 95 | * X/DIV = -(X + DIV)/DIV - 1, and X + DIV is less negative than X so this is |
| 96 | * a safe negation; if -DIV < X < 0 then the result is zero; otherwise, X |
| 97 | * is nonnegative so the straightforward division is safe. Because DIV > 1, |
| 98 | * X/DIV is safe to negate, and we can apply the remaining divisions to it. |
| 99 | */ |
| 100 | #define MDW__SHIFT(x, div, d) \\ |
| 101 | ((x) >= 0 ? ((x)/div d) : \\ |
| 102 | (x) <= -(div) ? -((-((x) + (div))/(div) + 1) d) : 0) |
| 103 | |
| 104 | /* Extract the bottommost digit of X, as an integer: i.e., the value of |
| 105 | * abs(X) mod 10. This works even if X is negative, never tries to divide |
| 106 | * negative numbers, and doesn't try to divide the most-negative value. |
| 107 | */ |
| 108 | #define MDW__RAW_DIGIT(x) (((x) < 0 ? -((x) + 1) % 10 + 1 : (x)) % 10) |
| 109 | |
| 110 | /* Extract the bottommost digit of X, as a character; if X is zero, then |
| 111 | * produce a space instead. This avoids leading zeroes which can be |
| 112 | * misinterpreted by callers. |
| 113 | */ |
| 114 | #define MDW__TEXT_DIGIT(x) ((x) ? '0' + MDW__RAW_DIGIT(x) : ' ') |
| 115 | |
| 116 | /* Extract the bottommost digit of the probe value, after dividing by DIV |
| 117 | * and applying the divisons D. |
| 118 | */ |
| 119 | #define MDW__DIGIT(div, d) \\ |
| 120 | MDW__TEXT_DIGIT(MDW__SHIFT(MDW__PROBE_EXPR, div, d)) |
| 121 | |
| 122 | /* Extract the bottommost six digits of the probe value after dividing by 10 |
| 123 | * and then applying the divisions D. |
| 124 | */ |
| 125 | #define MDW__9DIGITS(d) \\ |
| 126 | MDW__DIGIT(1000000000, d), \\ |
| 127 | MDW__DIGIT( 100000000, d), \\ |
| 128 | MDW__DIGIT( 10000000, d), \\ |
| 129 | MDW__DIGIT( 1000000, d), \\ |
| 130 | MDW__DIGIT( 100000, d), \\ |
| 131 | MDW__DIGIT( 10000, d), \\ |
| 132 | MDW__DIGIT( 1000, d), \\ |
| 133 | MDW__DIGIT( 100, d), \\ |
| 134 | MDW__DIGIT( 10, d) |
| 135 | |
| 136 | /* Increasingly huge divisions. PN divides by 10^(9*2^N). */ |
| 137 | #define MDW__P0 /MDW__G |
| 138 | #define MDW__P1 MDW__P0 MDW__P0 |
| 139 | #define MDW__P2 MDW__P1 MDW__P1 |
| 140 | #define MDW__P3 MDW__P2 MDW__P2 |
| 141 | #define MDW__P4 MDW__P3 MDW__P3 |
| 142 | #define MDW__P5 MDW__P4 MDW__P4 |
| 143 | |
| 144 | /* Increasingly long sequences of digits. DN(P) produces the 9 * 2^N |
| 145 | * digits after applying divisions P. |
| 146 | */ |
| 147 | #define MDW__D0(p) MDW__9DIGITS(p MDW__P0), MDW__9DIGITS(p MDW__E) |
| 148 | #define MDW__D1(p) MDW__D0(p MDW__P1), MDW__D0(p) |
| 149 | #define MDW__D2(p) MDW__D1(p MDW__P2), MDW__D1(p) |
| 150 | #define MDW__D3(p) MDW__D2(p MDW__P3), MDW__D2(p) |
| 151 | #define MDW__D4(p) MDW__D3(p MDW__P4), MDW__D3(p) |
| 152 | |
| 153 | /* Ensure that our exponential cascade is sufficient to represent the |
| 154 | * expression. |
| 155 | */ |
| 156 | MDW__ASSERT(MDW__SHIFT(MDW__PROBE_EXPR, 10, MDW__P5) == 0); |
| 157 | |
| 158 | /* Format the output. Everything is taken care of except the bottommost |
| 159 | * digit, which we handle seaprately because we actually want a \`leading' |
| 160 | * zero here if the constant value is actually zero. Format it so that |
| 161 | * we can extract it from the object file. |
| 162 | */ |
| 163 | const char mdw__probe_output[] = { |
| 164 | '\\n', |
| 165 | 'm', 'd', 'w', '-', |
| 166 | 'p', 'r', 'o', 'b', 'e', '-', |
| 167 | 'v', 'a', 'l', 'u', 'e', '=', '\"', |
| 168 | (MDW__PROBE_EXPR < 0 ? '-' : ' '), |
| 169 | MDW__D4(MDW__E), |
| 170 | '0' + MDW__RAW_DIGIT(MDW__PROBE_EXPR), |
| 171 | '\"', '\\n' |
| 172 | };]"]) |
| 173 | |
| 174 | AC_DEFUN([mdw_PROBE_CONSTANT], |
| 175 | [AC_REQUIRE([mdw__PROBE_CONSTANT_SETUP]) |
| 176 | AC_COMPILE_IFELSE([AC_LANG_SOURCE([[$3 |
| 177 | #define MDW__PROBE_EXPR ($2) |
| 178 | $mdw__probe_constant_body]])], |
| 179 | [$1=$(sed -n \ |
| 180 | 's:^mdw-probe-value="\(-\|\) *\([[0-9]]*\)"$:\1\2:p' conftest.o)], |
| 181 | [m4_if([$4], [], |
| 182 | [AC_MSG_FAILURE([failed to evaluate expression])], |
| 183 | [$4])])]) |