X-Git-Url: https://git.ozlabs.org/?p=ccan;a=blobdiff_plain;f=ccan%2Filog%2F_info;fp=ccan%2Filog%2F_info;h=2b4aeb2edded654b395bf9c6302e005b2d6944fd;hp=0000000000000000000000000000000000000000;hb=570c9c555f076e74f46141bb42b5d1d7ac89f632;hpb=8f61c0bccb152b2365baf70deac1e59264d7feb7

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+/**
+ * ilog - Integer logarithm.
+ *
+ * ILOG_32() and ILOG_64() compute the minimum number of bits required to store
+ *  an unsigned 32-bit or 64-bit value without any leading zero bits.
+ * This can also be thought of as the location of the highest set bit, with
+ *  counting starting from one (so that 0 returns 0, 1 returns 1, and 2**31
+ *  returns 32).
+ * When the value is known to be non-zero ILOGNZ_32() and ILOGNZ_64() can
+ *  compile into as few as two instructions, one of which may get optimized out
+ *  later.
+ * STATIC_ILOG_32 and STATIC_ILOG_64 allow computation on compile-time
+ *  constants, so other compile-time constants can be derived from them.
+ *
+ * Example:
+ *  #include <stdio.h>
+ *  #include <limits.h>
+ *  #include <ccan/ilog/ilog.h>
+ *
+ *  int main(void){
+ *    int i;
+ *    printf("ILOG_32(0x%08X)=%i\n",0,ILOG_32(0));
+ *    for(i=1;i<=STATIC_ILOG_32(USHRT_MAX);i++){
+ *      uint32_t v;
+ *      v=(uint32_t)1U<<i-1;
+ *      //Here we know v is non-zero, so we can use ILOGNZ_32().
+ *      printf("ILOG_32(0x%08X)=%i\n",v,ILOGNZ_32(v));
+ *    }
+ *    return 0;
+ *  }
+ *
+ * License: LGPL (v2 or later)
+ */
+#include <string.h>
+#include "config.h"
+
+int main(int _argc,const char *_argv[]){
+  /*Expect exactly one argument.*/
+  if(_argc!=2)return 1;
+  if(strcmp(_argv[1],"depends")==0){
+    /*PRINTF-CCAN-PACKAGES-YOU-NEED-ONE-PER-LINE-IF-ANY*/
+    return 0;
+  }
+  return 1;
+}