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Merge pull request #2087 from ziglang/float-parsing

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fix some hex literal parsing bugs
This commit is contained in:
Andrew Kelley 2019-03-22 10:16:46 -04:00 committed by GitHub
commit 3560f61c16
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2 changed files with 118 additions and 38 deletions
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74
src/tokenizer.cpp
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@ -326,51 +326,49 @@ static void end_float_token(Tokenize *t) {
return;
}
// A SoftFloat-3d float128 is represented internally as a standard
// quad-precision float with 15bit exponent and 113bit fractional.
// A SoftFloat-3e float128 is represented internally as a standard
// quad-precision float with 15bit exponent and 112bit fractional.
union { uint64_t repr[2]; float128_t actual; } f_bits;
if (bigint_cmp_zero(&t->significand) == CmpEQ) {
f_bits.repr[0] = 0;
f_bits.repr[1] = 0;
} else {
// normalize the significand
if (t->radix == 10) {
zig_panic("TODO: decimal floats");
} else {
int significand_magnitude_in_bin = 127 - bigint_clz(&t->significand, 128);
t->exponent_in_bin_or_dec += significand_magnitude_in_bin;
if (!(-16382 <= t->exponent_in_bin_or_dec && t->exponent_in_bin_or_dec <= 16383)) {
t->cur_tok->data.float_lit.overflow = true;
return;
}
uint64_t sig_bits[2] = {0, 0};
bigint_write_twos_complement(&t->significand, (uint8_t*) sig_bits, 128, false);
const uint64_t shift = 112 - significand_magnitude_in_bin;
const uint64_t exp_shift = 48;
// Mask the sign bit to 0 since always non-negative lex
const uint64_t exp_mask = 0xffffull << exp_shift;
// must be special-cased to avoid undefined behavior on shift == 64
if (shift == 128) {
f_bits.repr[0] = 0;
f_bits.repr[1] = sig_bits[0];
} else if (shift == 0) {
f_bits.repr[0] = sig_bits[0];
f_bits.repr[1] = sig_bits[1];
} else if (shift >= 64) {
f_bits.repr[0] = 0;
f_bits.repr[1] = sig_bits[0] << (shift - 64);
} else {
f_bits.repr[0] = sig_bits[0] << shift;
f_bits.repr[1] = (sig_bits[1] << shift) | (sig_bits[0] >> (64 - shift));
}
f_bits.repr[1] &= ~exp_mask;
f_bits.repr[1] |= (uint64_t)(t->exponent_in_bin_or_dec + 16383) << exp_shift;
int significand_magnitude_in_bin = 127 - bigint_clz(&t->significand, 128);
t->exponent_in_bin_or_dec += significand_magnitude_in_bin;
if (!(-16382 <= t->exponent_in_bin_or_dec && t->exponent_in_bin_or_dec <= 16383)) {
t->cur_tok->data.float_lit.overflow = true;
return;
}
// Shift bits of significand so they are left-justified at the 112-bit
// mark. We truncate excess bits and lose precision. No rounding.
//
// -16 <= shift <= 112
//
// NOTE: The loss of precision could be considered a limitation of using
// 128-bit floats. In stage2 we should use an arbitrary precision
// float/rational type to represent these and avoid this.
const int shift = 112 - significand_magnitude_in_bin;
bigint_write_twos_complement(&t->significand, (uint8_t*) f_bits.repr, 128, false);
if (shift >= 64) {
f_bits.repr[1] = f_bits.repr[0] << (shift - 64);
f_bits.repr[0] = 0;
} else if (shift > 0) {
f_bits.repr[1] = (f_bits.repr[1] << shift) | (f_bits.repr[0] >> (64 - shift));
f_bits.repr[0] = f_bits.repr[0] << shift;
} else if (shift < 0) {
int positive_shift = -shift;
assert(positive_shift <= 16);
f_bits.repr[0] = (f_bits.repr[0] >> positive_shift) | (f_bits.repr[1] << (64 - positive_shift));
f_bits.repr[1] = f_bits.repr[1] >> positive_shift;
}
// Lexer separates negative sign from value so this is always non-negative.
const uint64_t exp_mask = 0xffffull << 48;
f_bits.repr[1] &= ~exp_mask;
f_bits.repr[1] |= (uint64_t)(t->exponent_in_bin_or_dec + 16383) << 48;
}
bigfloat_init_128(&t->cur_tok->data.float_lit.bigfloat, f_bits.actual);

82
test/stage1/behavior/math.zig
View File

@ -307,6 +307,88 @@ test "quad hex float literal parsing accurate" {
// implied 1 is dropped, with an exponent of 0 (0x3fff) after biasing.
const expected: u128 = 0x3fff1111222233334444555566667777;
expect(@bitCast(u128, a) == expected);
// non-normalized
const b: f128 = 0x11.111222233334444555566667777p-4;
expect(@bitCast(u128, b) == expected);
const S = struct {
fn doTheTest() void {
{
var f: f128 = 0x1.2eab345678439abcdefea56782346p+5;
expect(@bitCast(u128, f) == 0x40042eab345678439abcdefea5678234);
}
{
var f: f128 = 0x1.edcb34a235253948765432134674fp-1;
expect(@bitCast(u128, f) == 0x3ffeedcb34a235253948765432134674);
}
{
var f: f128 = 0x1.353e45674d89abacc3a2ebf3ff4ffp-50;
expect(@bitCast(u128, f) == 0x3fcd353e45674d89abacc3a2ebf3ff4f);
}
{
var f: f128 = 0x1.ed8764648369535adf4be3214567fp-9;
expect(@bitCast(u128, f) == 0x3ff6ed8764648369535adf4be3214567);
}
const exp2ft = []f64{
0x1.6a09e667f3bcdp-1,
0x1.7a11473eb0187p-1,
0x1.8ace5422aa0dbp-1,
0x1.9c49182a3f090p-1,
0x1.ae89f995ad3adp-1,
0x1.c199bdd85529cp-1,
0x1.d5818dcfba487p-1,
0x1.ea4afa2a490dap-1,
0x1.0000000000000p+0,
0x1.0b5586cf9890fp+0,
0x1.172b83c7d517bp+0,
0x1.2387a6e756238p+0,
0x1.306fe0a31b715p+0,
0x1.3dea64c123422p+0,
0x1.4bfdad5362a27p+0,
0x1.5ab07dd485429p+0,
0x1.8p23,
0x1.62e430p-1,
0x1.ebfbe0p-3,
0x1.c6b348p-5,
0x1.3b2c9cp-7,
0x1.0p127,
-0x1.0p-149,
};
const answers = []u64{
0x3fe6a09e667f3bcd,
0x3fe7a11473eb0187,
0x3fe8ace5422aa0db,
0x3fe9c49182a3f090,
0x3feae89f995ad3ad,
0x3fec199bdd85529c,
0x3fed5818dcfba487,
0x3feea4afa2a490da,
0x3ff0000000000000,
0x3ff0b5586cf9890f,
0x3ff172b83c7d517b,
0x3ff2387a6e756238,
0x3ff306fe0a31b715,
0x3ff3dea64c123422,
0x3ff4bfdad5362a27,
0x3ff5ab07dd485429,
0x4168000000000000,
0x3fe62e4300000000,
0x3fcebfbe00000000,
0x3fac6b3480000000,
0x3f83b2c9c0000000,
0x47e0000000000000,
0xb6a0000000000000,
};
for (exp2ft) |x, i| {
expect(@bitCast(u64, x) == answers[i]);
}
}
};
S.doTheTest();
comptime S.doTheTest();
}
test "hex float literal within range" {