Skip to content

Commit

Permalink
[libc] simplify printf float writing
Browse files Browse the repository at this point in the history 
The two decimal float printing styles are similar, but different in how
they end. For simplicity of writing I initially gave them different
"write_last_block" functions. This patch unifies them into one function.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D158036
  • Loading branch information
@michaelrj-google
michaelrj-google committed Sep 13, 2023
1 parent 2a904f4 commit 3fb63c2
Showing 1 changed file with 77 additions and 139 deletions.
216 changes: 77 additions & 139 deletions libc/src/stdio/printf_core/float_dec_converter.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -299,100 +299,11 @@ class FloatWriter {
return 0;
}

int write_last_block_dec(BlockInt block, size_t block_digits,
RoundDirection round) {
char end_buff[BLOCK_SIZE];

const DecimalString buf(block + (MAX_BLOCK + 1));
const cpp::string_view int_to_str = buf.view();

// copy the last block_digits characters into the start of end_buff.
// TODO: Replace with memcpy
for (size_t count = 0; count < block_digits; ++count) {
end_buff[count] = int_to_str[count + 1 + (BLOCK_SIZE - block_digits)];
}

char low_digit = '0';
if (block_digits > 0) {
low_digit = end_buff[block_digits - 1];
} else if (max_block_count > 0) {
low_digit = '9';
} else if (buffered_digits > 0) {
low_digit = block_buffer[buffered_digits - 1];
}

bool round_up_max_blocks = false;

// Round up
if (round == RoundDirection::Up ||
(round == RoundDirection::Even && low_digit % 2 != 0)) {
bool has_carry = true;
round_up_max_blocks = true; // if we're rounding up, we might need to
// round up the max blocks that are buffered.
// handle the low block that we're adding
for (int count = static_cast<int>(block_digits) - 1;
count >= 0 && has_carry; --count) {
if (end_buff[count] == '9') {
end_buff[count] = '0';
} else {
end_buff[count] += 1;
has_carry = false;
round_up_max_blocks = false; // If the low block isn't all nines, then
// the max blocks aren't rounded up.
}
}
// handle the high block that's buffered
for (int count = static_cast<int>(buffered_digits) - 1;
count >= 0 && has_carry; --count) {
if (block_buffer[count] == '9') {
block_buffer[count] = '0';
} else {
block_buffer[count] += 1;
has_carry = false;
}
}

// has_carry should only be true here if every previous digit is 9, which
// implies that the number has never been written.
if (has_carry /* && !has_written */) {
++total_digits;
++digits_before_decimal;
// Normally write_left_padding is called by flush_buffer but since we're
// rounding up all of the digits, the ones in the buffer are wrong and
// can't be flushed.
RET_IF_RESULT_NEGATIVE(
padding_writer.write_left_padding(writer, total_digits));
// Now we know we need to print a leading 1, zeroes up to the decimal
// point, the decimal point, and then finally digits after it.
RET_IF_RESULT_NEGATIVE(writer->write('1'));
// digits_before_decimal - 1 to account for the leading '1'
RET_IF_RESULT_NEGATIVE(writer->write('0', digits_before_decimal - 1));
if (has_decimal_point) {
RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
// add one to digits_before_decimal to account for the decimal point
// itself.
if (total_digits > digits_before_decimal + 1) {
RET_IF_RESULT_NEGATIVE(
writer->write('0', total_digits - (digits_before_decimal + 1)));
}
}
total_digits_written = total_digits;
return 0;
}
}
// Either we intend to round down, or the rounding up is complete. Flush the
// buffers.

RET_IF_RESULT_NEGATIVE(flush_buffer(round_up_max_blocks));
int write_last_block(BlockInt block, size_t block_digits,
RoundDirection round, int exponent = 0,
char exp_char = '\0') {
bool has_exp = (exp_char != '\0');

// And then write the final block.
RET_IF_RESULT_NEGATIVE(writer->write({end_buff, block_digits}));
total_digits_written += block_digits;
return 0;
}

int write_last_block_exp(uint32_t block, size_t block_digits,
RoundDirection round, int exponent, char exp_char) {
char end_buff[BLOCK_SIZE];

{
Expand Down Expand Up @@ -450,48 +361,74 @@ class FloatWriter {
// has_carry should only be true here if every previous digit is 9, which
// implies that the number has never been written.
if (has_carry /* && !has_written */) {
// Since this is exponential notation, we don't write any more digits
// but we do increment the exponent.
++exponent;

const ExponentString buf(exponent);
const cpp::string_view int_to_str = buf.view();

// TODO: also change this to calculate the width of the number more
// efficiently.
size_t exponent_width = int_to_str.size();
size_t number_digits =
buffered_digits + (max_block_count * BLOCK_SIZE) + block_digits;

// Here we have to recalculate the total number of digits since the
// exponent's width may have changed. We're only adding 1 to exponent
// width since exp_str appends the sign.
total_digits =
(has_decimal_point ? 1 : 0) + number_digits + 1 + exponent_width;

// Normally write_left_padding is called by flush_buffer but since we're
// rounding up all of the digits, the ones in the buffer are wrong and
// can't be flushed.
RET_IF_RESULT_NEGATIVE(
padding_writer.write_left_padding(writer, total_digits));
// Now we know we need to print a leading 1, the decimal point, and then
// zeroes after it.
RET_IF_RESULT_NEGATIVE(writer->write('1'));
// digits_before_decimal - 1 to account for the leading '1'
if (has_decimal_point) {
RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
// This is just the length of the number, not including the decimal
// point, or exponent.

if (number_digits > 1) {
RET_IF_RESULT_NEGATIVE(writer->write('0', number_digits - 1));
if (has_exp) { // This is in %e style
// Since this is exponential notation, we don't write any more digits
// but we do increment the exponent.
++exponent;

const ExponentString buf(exponent);
const cpp::string_view int_to_str = buf.view();

// TODO: also change this to calculate the width of the number more
// efficiently.
size_t exponent_width = int_to_str.size();
size_t number_digits =
buffered_digits + (max_block_count * BLOCK_SIZE) + block_digits;

// Here we have to recalculate the total number of digits since the
// exponent's width may have changed. We're only adding 1 to exponent
// width since exp_str appends the sign.
total_digits =
(has_decimal_point ? 1 : 0) + number_digits + 1 + exponent_width;

// Normally write_left_padding is called by flush_buffer but since
// we're rounding up all of the digits, the ones in the buffer are
// wrong and can't be flushed.
RET_IF_RESULT_NEGATIVE(
padding_writer.write_left_padding(writer, total_digits));
// Now we know we need to print a leading 1, the decimal point, and
// then zeroes after it.
RET_IF_RESULT_NEGATIVE(writer->write('1'));
// digits_before_decimal - 1 to account for the leading '1'
if (has_decimal_point) {
RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
// This is just the length of the number, not including the decimal
// point, or exponent.

if (number_digits > 1) {
RET_IF_RESULT_NEGATIVE(writer->write('0', number_digits - 1));
}
}
RET_IF_RESULT_NEGATIVE(writer->write(exp_char));
RET_IF_RESULT_NEGATIVE(writer->write(int_to_str));

total_digits_written = total_digits;
return WRITE_OK;
} else { // This is in %f style
++total_digits;
++digits_before_decimal;
// Normally write_left_padding is called by flush_buffer but since
// we're rounding up all of the digits, the ones in the buffer are
// wrong and can't be flushed.
RET_IF_RESULT_NEGATIVE(
padding_writer.write_left_padding(writer, total_digits));
// Now we know we need to print a leading 1, zeroes up to the decimal
// point, the decimal point, and then finally digits after it.
RET_IF_RESULT_NEGATIVE(writer->write('1'));
// digits_before_decimal - 1 to account for the leading '1'
RET_IF_RESULT_NEGATIVE(writer->write('0', digits_before_decimal - 1));
if (has_decimal_point) {
RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
// add one to digits_before_decimal to account for the decimal point
// itself.
if (total_digits > digits_before_decimal + 1) {
RET_IF_RESULT_NEGATIVE(writer->write(
'0', total_digits - (digits_before_decimal + 1)));
}
}
total_digits_written = total_digits;
return WRITE_OK;
}
RET_IF_RESULT_NEGATIVE(writer->write(exp_char));
RET_IF_RESULT_NEGATIVE(writer->write(int_to_str));

total_digits_written = total_digits;
return WRITE_OK;
}
}
// Either we intend to round down, or the rounding up is complete. Flush the
Expand All @@ -509,10 +446,11 @@ class FloatWriter {
buffered_digits = block_digits;
RET_IF_RESULT_NEGATIVE(flush_buffer());

RET_IF_RESULT_NEGATIVE(writer->write(exp_char));
const ExponentString buf(exponent);
RET_IF_RESULT_NEGATIVE(writer->write(buf.view()));

if (has_exp) {
RET_IF_RESULT_NEGATIVE(writer->write(exp_char));
const ExponentString buf(exponent);
RET_IF_RESULT_NEGATIVE(writer->write(buf.view()));
}
total_digits_written = total_digits;

return WRITE_OK;
Expand Down Expand Up @@ -634,7 +572,7 @@ LIBC_INLINE int convert_float_decimal_typed(Writer *writer,
round = get_round_direction(last_digit, truncated, is_negative);

RET_IF_RESULT_NEGATIVE(
float_writer.write_last_block_dec(digits, maximum, round));
float_writer.write_last_block(digits, maximum, round));
break;
}
}
Expand Down Expand Up @@ -800,7 +738,7 @@ LIBC_INLINE int convert_float_dec_exp_typed(Writer *writer,
}
round = get_round_direction(last_digit, truncated, is_negative);

RET_IF_RESULT_NEGATIVE(float_writer.write_last_block_exp(
RET_IF_RESULT_NEGATIVE(float_writer.write_last_block(
digits, maximum, round, final_exponent, a + 'E' - 'A'));

RET_IF_RESULT_NEGATIVE(float_writer.right_pad());
Expand Down

0 comments on commit 3fb63c2

Please sign in to comment.