diff options
Diffstat (limited to 'libguile/symbols.c')
-rw-r--r-- | libguile/symbols.c | 50 |
1 files changed, 39 insertions, 11 deletions
diff --git a/libguile/symbols.c b/libguile/symbols.c index 9cb300ab0..9dd204478 100644 --- a/libguile/symbols.c +++ b/libguile/symbols.c @@ -33,6 +33,7 @@ #include "libguile/variable.h" #include "libguile/alist.h" #include "libguile/fluids.h" +#include "libguile/threads.h" #include "libguile/strings.h" #include "libguile/vectors.h" #include "libguile/weak-set.h" @@ -378,7 +379,9 @@ SCM_DEFINE (scm_string_ci_to_symbol, "string-ci->symbol", 1, 0, 0, /* The default prefix for `gensym'd symbols. */ static SCM default_gensym_prefix; -#define MAX_PREFIX_LENGTH 30 +#define GENSYM_LENGTH 22 /* bytes */ +#define GENSYM_RADIX_BITS 6 +#define GENSYM_RADIX (1 << (GENSYM_RADIX_BITS)) SCM_DEFINE (scm_gensym, "gensym", 0, 1, 0, (SCM prefix), @@ -389,22 +392,47 @@ SCM_DEFINE (scm_gensym, "gensym", 0, 1, 0, "resetting the counter.") #define FUNC_NAME s_scm_gensym { - static int gensym_counter = 0; - + static const char base64[GENSYM_RADIX] = + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789$@"; + static const char base4[4] = "_.-~"; + + unsigned char *digit_buf = SCM_I_CURRENT_THREAD->gensym_counter; + char char_buf[GENSYM_LENGTH]; SCM suffix, name; - int n, n_digits; - char buf[SCM_INTBUFLEN]; + int i; if (SCM_UNBNDP (prefix)) prefix = default_gensym_prefix; - /* mutex in case another thread looks and incs at the exact same moment */ - scm_i_scm_pthread_mutex_lock (&scm_i_misc_mutex); - n = gensym_counter++; - scm_i_pthread_mutex_unlock (&scm_i_misc_mutex); + if (SCM_UNLIKELY (digit_buf == NULL)) + { + /* This is the first time gensym has been called in this thread. + Allocate and randomize our new thread-local gensym counter */ + digit_buf = (unsigned char *) + scm_gc_malloc_pointerless (GENSYM_LENGTH, "gensym-counter"); + scm_i_random_bytes_from_platform (digit_buf, GENSYM_LENGTH); + for (i = (GENSYM_LENGTH - 1); i >= 0; --i) + digit_buf[i] &= (GENSYM_RADIX - 1); + SCM_I_CURRENT_THREAD->gensym_counter = digit_buf; + } + + /* Increment our thread-local gensym_counter. */ + for (i = (GENSYM_LENGTH - 1); i >= 0; --i) + { + if (SCM_LIKELY (++(digit_buf[i]) < GENSYM_RADIX)) + break; + else + digit_buf[i] = 0; + } + + /* Encode digit_buf as base64, except for the first character where we + use the sparse glyphs "_.-~" (base 4) to provide some visual + separation between the prefix and the dense base64 block. */ + for (i = (GENSYM_LENGTH - 1); i > 0; --i) + char_buf[i] = base64[digit_buf[i]]; + char_buf[0] = base4[digit_buf[0] & 3]; - n_digits = scm_iint2str (n, 10, buf); - suffix = scm_from_latin1_stringn (buf, n_digits); + suffix = scm_from_latin1_stringn (char_buf, GENSYM_LENGTH); name = scm_string_append (scm_list_2 (prefix, suffix)); return scm_string_to_symbol (name); } |