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rc: avoid undefined C There are two bugs in pdec() on INT_MIN: * wrong output. `n = 1-n' should be `n = -1-n' when n is INT_MIN. * infinite loop. gcc optimizes `if(n>=0)' into `if(true)' because `-INT_MIN' (signed integer overflow) is undefined behavior in C, and gcc assumes the negation of a negative number must be positive. The resulting binary keeps printing '-' forever given INT_MIN. Try the simplified pdec.c below. $ gcc pdec.c $ ./a.out -2147483648 --214748364* $ gcc pdec.c -O2 $ ./a.out -2147483648 <infinite loop> $ gcc pdec.c -O2 -D__PATCH__ $ ./a.out -2147483648 -2147483648 === pdec.c === #include <stdio.h> #include <stdlib.h> #include <limits.h> #define io void void pchr(io *f, int c) { putchar(c); } void pdec(io *f, int n) { if(n<0){ #ifndef __PATCH__ n=-n; if(n>=0){ pchr(f, '-'); pdec(f, n); return; } /* n is two's complement minimum integer */ n = 1-n; #else if(n!=INT_MIN){ pchr(f, '-'); pdec(f, -n); return; } /* n is two's complement minimum integer */ n = -(INT_MIN+1); #endif pchr(f, '-'); pdec(f, n/10); pchr(f, n%10+'1'); return; } if(n>9) pdec(f, n/10); pchr(f, n%10+'0'); } int main(int argc, char **argv) { int n = atoi(argv[1]); pdec(NULL, n); putchar('\n'); } R=rsc CC=plan9port.codebot https://codereview.appspot.com/7241055
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  1 1bfec89b 2013-03-19 rsc #include <limits.h>

  2 f08fdedc 2003-11-23 devnull #include "rc.h"

  3 f08fdedc 2003-11-23 devnull #include "exec.h"

  4 f08fdedc 2003-11-23 devnull #include "io.h"

  5 f08fdedc 2003-11-23 devnull #include "fns.h"

  6 c8f53842 2007-03-26 devnull int pfmtnest = 0;

  7 c8f53842 2007-03-26 devnull 

  8 c8f53842 2007-03-26 devnull void

  9 c8f53842 2007-03-26 devnull pfmt(io *f, char *fmt, ...)

 10 c8f53842 2007-03-26 devnull {

 11 f08fdedc 2003-11-23 devnull 	va_list ap;

 12 f08fdedc 2003-11-23 devnull 	char err[ERRMAX];

 13 f08fdedc 2003-11-23 devnull 	va_start(ap, fmt);

 14 f08fdedc 2003-11-23 devnull 	pfmtnest++;

 15 f08fdedc 2003-11-23 devnull 	for(;*fmt;fmt++)

 16 c8f53842 2007-03-26 devnull 		if(*fmt!='%')

 17 c8f53842 2007-03-26 devnull 			pchr(f, *fmt);

 18 f08fdedc 2003-11-23 devnull 		else switch(*++fmt){

 19 c8f53842 2007-03-26 devnull 		case '\0':

 20 c8f53842 2007-03-26 devnull 			va_end(ap);

 21 c8f53842 2007-03-26 devnull 			return;

 22 c8f53842 2007-03-26 devnull 		case 'c':

 23 c8f53842 2007-03-26 devnull 			pchr(f, va_arg(ap, int));

 24 c8f53842 2007-03-26 devnull 			break;

 25 c8f53842 2007-03-26 devnull 		case 'd':

 26 c8f53842 2007-03-26 devnull 			pdec(f, va_arg(ap, int));

 27 c8f53842 2007-03-26 devnull 			break;

 28 c8f53842 2007-03-26 devnull 		case 'o':

 29 c8f53842 2007-03-26 devnull 			poct(f, va_arg(ap, unsigned));

 30 c8f53842 2007-03-26 devnull 			break;

 31 c8f53842 2007-03-26 devnull 		case 'p':

 32 c8f53842 2007-03-26 devnull 			pptr(f, va_arg(ap, void*));

 33 c8f53842 2007-03-26 devnull 			break;

 34 c8f53842 2007-03-26 devnull 		case 'Q':

 35 c8f53842 2007-03-26 devnull 			pquo(f, va_arg(ap, char *));

 36 c8f53842 2007-03-26 devnull 			break;

 37 c8f53842 2007-03-26 devnull 		case 'q':

 38 c8f53842 2007-03-26 devnull 			pwrd(f, va_arg(ap, char *));

 39 c8f53842 2007-03-26 devnull 			break;

 40 c8f53842 2007-03-26 devnull 		case 'r':

 41 40402738 2007-03-26 devnull 			rerrstr(err, sizeof err); pstr(f, err);

 42 c8f53842 2007-03-26 devnull 			break;

 43 c8f53842 2007-03-26 devnull 		case 's':

 44 c8f53842 2007-03-26 devnull 			pstr(f, va_arg(ap, char *));

 45 c8f53842 2007-03-26 devnull 			break;

 46 c8f53842 2007-03-26 devnull 		case 't':

 47 c8f53842 2007-03-26 devnull 			pcmd(f, va_arg(ap, struct tree *));

 48 c8f53842 2007-03-26 devnull 			break;

 49 c8f53842 2007-03-26 devnull 		case 'v':

 50 c8f53842 2007-03-26 devnull 			pval(f, va_arg(ap, struct word *));

 51 c8f53842 2007-03-26 devnull 			break;

 52 c8f53842 2007-03-26 devnull 		default:

 53 c8f53842 2007-03-26 devnull 			pchr(f, *fmt);

 54 c8f53842 2007-03-26 devnull 			break;

 55 f08fdedc 2003-11-23 devnull 		}

 56 f08fdedc 2003-11-23 devnull 	va_end(ap);

 57 c8f53842 2007-03-26 devnull 	if(--pfmtnest==0)

 58 c8f53842 2007-03-26 devnull 		flush(f);

 59 f08fdedc 2003-11-23 devnull }

 60 c8f53842 2007-03-26 devnull 

 61 c8f53842 2007-03-26 devnull void

 62 c8f53842 2007-03-26 devnull pchr(io *b, int c)

 63 f08fdedc 2003-11-23 devnull {

 64 c8f53842 2007-03-26 devnull 	if(b->bufp==b->ebuf)

 65 c8f53842 2007-03-26 devnull 		fullbuf(b, c);

 66 f08fdedc 2003-11-23 devnull 	else *b->bufp++=c;

 67 f08fdedc 2003-11-23 devnull }

 68 c8f53842 2007-03-26 devnull 

 69 c8f53842 2007-03-26 devnull int

 70 c8f53842 2007-03-26 devnull rchr(io *b)

 71 f08fdedc 2003-11-23 devnull {

 72 c8f53842 2007-03-26 devnull 	if(b->bufp==b->ebuf)

 73 c8f53842 2007-03-26 devnull 		return emptybuf(b);

 74 f08fdedc 2003-11-23 devnull 	return *b->bufp++ & 0xFF;

 75 f08fdedc 2003-11-23 devnull }

 76 f08fdedc 2003-11-23 devnull 

 77 c8f53842 2007-03-26 devnull void

 78 c8f53842 2007-03-26 devnull pquo(io *f, char *s)

 79 f08fdedc 2003-11-23 devnull {

 80 f08fdedc 2003-11-23 devnull 	pchr(f, '\'');

 81 f08fdedc 2003-11-23 devnull 	for(;*s;s++)

 82 c8f53842 2007-03-26 devnull 		if(*s=='\'')

 83 c8f53842 2007-03-26 devnull 			pfmt(f, "''");

 84 f08fdedc 2003-11-23 devnull 		else pchr(f, *s);

 85 f08fdedc 2003-11-23 devnull 	pchr(f, '\'');

 86 f08fdedc 2003-11-23 devnull }

 87 c8f53842 2007-03-26 devnull 

 88 c8f53842 2007-03-26 devnull void

 89 c8f53842 2007-03-26 devnull pwrd(io *f, char *s)

 90 f08fdedc 2003-11-23 devnull {

 91 f08fdedc 2003-11-23 devnull 	char *t;

 92 c8f53842 2007-03-26 devnull 	for(t = s;*t;t++) if(!wordchr(*t)) break;

 93 c8f53842 2007-03-26 devnull 	if(t==s || *t)

 94 c8f53842 2007-03-26 devnull 		pquo(f, s);

 95 f08fdedc 2003-11-23 devnull 	else pstr(f, s);

 96 f08fdedc 2003-11-23 devnull }

 97 c8f53842 2007-03-26 devnull 

 98 c8f53842 2007-03-26 devnull void

 99 c8f53842 2007-03-26 devnull pptr(io *f, void *v)

100 f08fdedc 2003-11-23 devnull {

101 f08fdedc 2003-11-23 devnull 	int n;

102 c8f53842 2007-03-26 devnull 	uintptr p;

103 c8f53842 2007-03-26 devnull 

104 c8f53842 2007-03-26 devnull 	p = (uintptr)v;

105 c8f53842 2007-03-26 devnull 	if(sizeof(uintptr) == sizeof(uvlong) && p>>32)

106 c8f53842 2007-03-26 devnull 		for(n = 60;n>=32;n-=4) pchr(f, "0123456789ABCDEF"[(p>>n)&0xF]);

107 c8f53842 2007-03-26 devnull 

108 c8f53842 2007-03-26 devnull 	for(n = 28;n>=0;n-=4) pchr(f, "0123456789ABCDEF"[(p>>n)&0xF]);

109 f08fdedc 2003-11-23 devnull }

110 c8f53842 2007-03-26 devnull 

111 c8f53842 2007-03-26 devnull void

112 c8f53842 2007-03-26 devnull pstr(io *f, char *s)

113 f08fdedc 2003-11-23 devnull {

114 c8f53842 2007-03-26 devnull 	if(s==0)

115 c8f53842 2007-03-26 devnull 		s="(null)";

116 f08fdedc 2003-11-23 devnull 	while(*s) pchr(f, *s++);

117 f08fdedc 2003-11-23 devnull }

118 c8f53842 2007-03-26 devnull 

119 c8f53842 2007-03-26 devnull void

120 c8f53842 2007-03-26 devnull pdec(io *f, int n)

121 f08fdedc 2003-11-23 devnull {

122 f08fdedc 2003-11-23 devnull 	if(n<0){

123 1bfec89b 2013-03-19 rsc 		if(n!=INT_MIN){

124 f08fdedc 2003-11-23 devnull 			pchr(f, '-');

125 1bfec89b 2013-03-19 rsc 			pdec(f, -n);

126 f08fdedc 2003-11-23 devnull 			return;

127 f08fdedc 2003-11-23 devnull 		}

128 f08fdedc 2003-11-23 devnull 		/* n is two's complement minimum integer */

129 1bfec89b 2013-03-19 rsc 		n = -(INT_MIN+1);

130 f08fdedc 2003-11-23 devnull 		pchr(f, '-');

131 f08fdedc 2003-11-23 devnull 		pdec(f, n/10);

132 f08fdedc 2003-11-23 devnull 		pchr(f, n%10+'1');

133 f08fdedc 2003-11-23 devnull 		return;

134 f08fdedc 2003-11-23 devnull 	}

135 c8f53842 2007-03-26 devnull 	if(n>9)

136 c8f53842 2007-03-26 devnull 		pdec(f, n/10);

137 f08fdedc 2003-11-23 devnull 	pchr(f, n%10+'0');

138 f08fdedc 2003-11-23 devnull }

139 c8f53842 2007-03-26 devnull 

140 c8f53842 2007-03-26 devnull void

141 c8f53842 2007-03-26 devnull poct(io *f, unsigned n)

142 f08fdedc 2003-11-23 devnull {

143 c8f53842 2007-03-26 devnull 	if(n>7)

144 c8f53842 2007-03-26 devnull 		poct(f, n>>3);

145 f08fdedc 2003-11-23 devnull 	pchr(f, (n&7)+'0');

146 f08fdedc 2003-11-23 devnull }

147 c8f53842 2007-03-26 devnull 

148 c8f53842 2007-03-26 devnull void

149 c8f53842 2007-03-26 devnull pval(io *f, word *a)

150 f08fdedc 2003-11-23 devnull {

151 f08fdedc 2003-11-23 devnull 	if(a){

152 f08fdedc 2003-11-23 devnull 		while(a->next && a->next->word){

153 f08fdedc 2003-11-23 devnull 			pwrd(f, a->word);

154 f08fdedc 2003-11-23 devnull 			pchr(f, ' ');

155 c8f53842 2007-03-26 devnull 			a = a->next;

156 f08fdedc 2003-11-23 devnull 		}

157 f08fdedc 2003-11-23 devnull 		pwrd(f, a->word);

158 f08fdedc 2003-11-23 devnull 	}

159 f08fdedc 2003-11-23 devnull }

160 c8f53842 2007-03-26 devnull 

161 c8f53842 2007-03-26 devnull int

162 c8f53842 2007-03-26 devnull fullbuf(io *f, int c)

163 f08fdedc 2003-11-23 devnull {

164 f08fdedc 2003-11-23 devnull 	flush(f);

165 f08fdedc 2003-11-23 devnull 	return *f->bufp++=c;

166 f08fdedc 2003-11-23 devnull }

167 c8f53842 2007-03-26 devnull 

168 c8f53842 2007-03-26 devnull void

169 c8f53842 2007-03-26 devnull flush(io *f)

170 f08fdedc 2003-11-23 devnull {

171 f08fdedc 2003-11-23 devnull 	int n;

172 f08fdedc 2003-11-23 devnull 	char *s;

173 f08fdedc 2003-11-23 devnull 	if(f->strp){

174 c8f53842 2007-03-26 devnull 		n = f->ebuf-f->strp;

175 c8f53842 2007-03-26 devnull 		f->strp = realloc(f->strp, n+101);

176 c8f53842 2007-03-26 devnull 		if(f->strp==0)

177 c8f53842 2007-03-26 devnull 			panic("Can't realloc %d bytes in flush!", n+101);

178 c8f53842 2007-03-26 devnull 		f->bufp = f->strp+n;

179 c8f53842 2007-03-26 devnull 		f->ebuf = f->bufp+100;

180 c8f53842 2007-03-26 devnull 		for(s = f->bufp;s<=f->ebuf;s++) *s='\0';

181 f08fdedc 2003-11-23 devnull 	}

182 f08fdedc 2003-11-23 devnull 	else{

183 c8f53842 2007-03-26 devnull 		n = f->bufp-f->buf;

184 f08fdedc 2003-11-23 devnull 		if(n && Write(f->fd, f->buf, n) < 0){

185 f08fdedc 2003-11-23 devnull 			Write(3, "Write error\n", 12);

186 c8f53842 2007-03-26 devnull 			if(ntrap)

187 c8f53842 2007-03-26 devnull 				dotrap();

188 f08fdedc 2003-11-23 devnull 		}

189 c8f53842 2007-03-26 devnull 		f->bufp = f->buf;

190 c8f53842 2007-03-26 devnull 		f->ebuf = f->buf+NBUF;

191 f08fdedc 2003-11-23 devnull 	}

192 f08fdedc 2003-11-23 devnull }

193 c8f53842 2007-03-26 devnull 

194 c8f53842 2007-03-26 devnull io*

195 c8f53842 2007-03-26 devnull openfd(int fd)

196 c8f53842 2007-03-26 devnull {

197 c8f53842 2007-03-26 devnull 	io *f = new(struct io);

198 c8f53842 2007-03-26 devnull 	f->fd = fd;

199 c8f53842 2007-03-26 devnull 	f->bufp = f->ebuf = f->buf;

200 c8f53842 2007-03-26 devnull 	f->strp = 0;

201 f08fdedc 2003-11-23 devnull 	return f;

202 f08fdedc 2003-11-23 devnull }

203 c8f53842 2007-03-26 devnull 

204 c8f53842 2007-03-26 devnull io*

205 c8f53842 2007-03-26 devnull openstr(void)

206 c8f53842 2007-03-26 devnull {

207 c8f53842 2007-03-26 devnull 	io *f = new(struct io);

208 f08fdedc 2003-11-23 devnull 	char *s;

209 f08fdedc 2003-11-23 devnull 	f->fd=-1;

210 c8f53842 2007-03-26 devnull 	f->bufp = f->strp = emalloc(101);

211 c8f53842 2007-03-26 devnull 	f->ebuf = f->bufp+100;

212 c8f53842 2007-03-26 devnull 	for(s = f->bufp;s<=f->ebuf;s++) *s='\0';

213 f08fdedc 2003-11-23 devnull 	return f;

214 f08fdedc 2003-11-23 devnull }

215 f08fdedc 2003-11-23 devnull /*

216 f08fdedc 2003-11-23 devnull  * Open a corebuffer to read.  EOF occurs after reading len

217 f08fdedc 2003-11-23 devnull  * characters from buf.

218 f08fdedc 2003-11-23 devnull  */

219 c8f53842 2007-03-26 devnull 

220 c8f53842 2007-03-26 devnull io*

221 c8f53842 2007-03-26 devnull opencore(char *s, int len)

222 f08fdedc 2003-11-23 devnull {

223 c8f53842 2007-03-26 devnull 	io *f = new(struct io);

224 c8f53842 2007-03-26 devnull 	char *buf = emalloc(len);

225 f08fdedc 2003-11-23 devnull 	f->fd= -1 /*open("/dev/null", 0)*/;

226 c8f53842 2007-03-26 devnull 	f->bufp = f->strp = buf;

227 c8f53842 2007-03-26 devnull 	f->ebuf = buf+len;

228 f08fdedc 2003-11-23 devnull 	Memcpy(buf, s, len);

229 f08fdedc 2003-11-23 devnull 	return f;

230 f08fdedc 2003-11-23 devnull }

231 c8f53842 2007-03-26 devnull 

232 c8f53842 2007-03-26 devnull void

233 2894c70c 2007-03-26 devnull iorewind(io *io)

234 f08fdedc 2003-11-23 devnull {

235 c8f53842 2007-03-26 devnull 	if(io->fd==-1)

236 c8f53842 2007-03-26 devnull 		io->bufp = io->strp;

237 f08fdedc 2003-11-23 devnull 	else{

238 c8f53842 2007-03-26 devnull 		io->bufp = io->ebuf = io->buf;

239 f08fdedc 2003-11-23 devnull 		Seek(io->fd, 0L, 0);

240 f08fdedc 2003-11-23 devnull 	}

241 f08fdedc 2003-11-23 devnull }

242 c8f53842 2007-03-26 devnull 

243 c8f53842 2007-03-26 devnull void

244 c8f53842 2007-03-26 devnull closeio(io *io)

245 f08fdedc 2003-11-23 devnull {

246 c8f53842 2007-03-26 devnull 	if(io->fd>=0)

247 c8f53842 2007-03-26 devnull 		close(io->fd);

248 c8f53842 2007-03-26 devnull 	if(io->strp)

249 c8f53842 2007-03-26 devnull 		efree(io->strp);

250 f08fdedc 2003-11-23 devnull 	efree((char *)io);

251 f08fdedc 2003-11-23 devnull }

252 c8f53842 2007-03-26 devnull 

253 c8f53842 2007-03-26 devnull int

254 c8f53842 2007-03-26 devnull emptybuf(io *f)

255 f08fdedc 2003-11-23 devnull {

256 f08fdedc 2003-11-23 devnull 	int n;

257 c8f53842 2007-03-26 devnull 	if(f->fd==-1 || (n = Read(f->fd, f->buf, NBUF))<=0) return EOF;

258 c8f53842 2007-03-26 devnull 	f->bufp = f->buf;

259 c8f53842 2007-03-26 devnull 	f->ebuf = f->buf+n;

260 f08fdedc 2003-11-23 devnull 	return *f->bufp++&0xff;

261 f08fdedc 2003-11-23 devnull }