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Parse strings without a temporary String: 3 → 2 objects per BigDecimal(str), ~18% faster #565

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Parse strings without a temporary String: 3 → 2 objects per BigDecimal(str), ~18% faster #565

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5be5aa4
Parse strings without allocating a temporary String
czj Oct 26, 2026
4a9c454
Check the first character inside bigdecimal_parse_special_string
czj Oct 27, 2026
cdb9348
Free the digit buffer before leaving VpAlloc on invalid input
czj Oct 27, 2026
cf3291c
Test that parsing a short string allocates only the result
czj Oct 27, 2026
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14 changes: 11 additions & 3 deletions ext/bigdecimal/bigdecimal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4155,6 +4155,14 @@ bigdecimal_parse_special_string(const char *str)
static const size_t table_length = sizeof(table) / sizeof(table[0]);
size_t i;

/* Fast path: every entry of the table starts with one of these */
switch (*str) {
case 'I': case 'N': case '+': case '-':
break;
default:
return (NULLABLE_BDVALUE) { Qnil, NULL };
}

for (i = 0; i < table_length; ++i) {
const char *p;
if (strncmp(str, table[i].str, table[i].len) != 0) {
Expand Down Expand Up @@ -4223,8 +4231,7 @@ VpAlloc(const char *szVal, int strict_p, int exc)
/* Scanning digits */

/* A buffer for keeping scanned digits */
buf = rb_str_tmp_new(strlen(szVal) + 1);
psz = RSTRING_PTR(buf);
psz = ALLOCV_N(char, buf, strlen(szVal) + 1);

/* cursor: i for psz, and j for szVal */
i = j = 0;
Expand Down Expand Up @@ -4364,6 +4371,7 @@ VpAlloc(const char *szVal, int strict_p, int exc)
if (strict_p && ((ni == 0 && nf == 0) || (exp_seen && ne == 0))) {
VALUE str;
invalid_value:
ALLOCV_END(buf);
if (!strict_p) {
BDVALUE res = rbd_allocate_struct_zero_wrap(1, 1);
return (NULLABLE_BDVALUE) { res.bigdecimal, res.real };
Expand All @@ -4381,7 +4389,7 @@ VpAlloc(const char *szVal, int strict_p, int exc)
Real *vp = VpPtr(obj);
VpSetZero(vp, sign);
VpCtoV(vp, psz, ni, psz + ipf, nf, psz + ipe, ne);
rb_str_resize(buf, 0);
ALLOCV_END(buf);
return (NULLABLE_BDVALUE) { obj, vp };
}

Expand Down
30 changes: 30 additions & 0 deletions test/bigdecimal/test_bigdecimal.rb
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Expand Up @@ -2256,6 +2256,36 @@ def test_split_under_gc_stress
EOS
end

def test_parse_long_string_under_gc_stress
paths = $LOAD_PATH.map{|path| "-I#{path}" }
assert_in_out_err([*paths, "-rbigdecimal", "--disable-gems"], <<-EOS, ["2001", "nil", "ArgumentError"], [])
GC.stress = true
p BigDecimal("1" + "0" * 2000).exponent
p BigDecimal("1" * 2000 + "x", exception: false)
begin
BigDecimal("1" * 2000 + "x")
rescue ArgumentError => e
puts e.class
end
EOS
end

def test_parse_string_allocations
omit "allocation counts are CRuby-specific" unless RUBY_ENGINE == "ruby"
paths = $LOAD_PATH.map{|path| "-I#{path}" }
assert_in_out_err([*paths, "-rbigdecimal", "-rbigdecimal/util", "--disable-gems"], <<-EOS, ["true", "true"], [])
def allocations
before = GC.stat(:total_allocated_objects)
yield
GC.stat(:total_allocated_objects) - before
end
BigDecimal("129.90")
"129.90".to_d
p allocations { 100.times { BigDecimal("129.90") } } < 250
p allocations { 100.times { "129.90".to_d } } < 250
EOS
end

def test_coerce_under_gc_stress
paths = $LOAD_PATH.map{|path| "-I#{path}" }
assert_in_out_err([*paths, "-rbigdecimal", "--disable-gems"], <<-EOS, [], [])
Expand Down