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SR-3131: Adjust choice of decimal vs. exponential format #15805

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Merged
merged 4 commits into from
Apr 12, 2018
Merged

SR-3131: Adjust choice of decimal vs. exponential format #15805

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ec7f7b0
SR-3131: Adjust choice of decimal vs. exponential format
tbkka Apr 6, 2018
ae7f7bb
Spell "Float80(1 << 64)" as "0x1.0p64L"
tbkka Apr 10, 2018
7d09c9d
Use 64-bit integers when computing numbers bigger than 2^32.
tbkka Apr 11, 2018
dd86067
Use hex float notation to clarify the Float and Double cutoffs
tbkka Apr 12, 2018
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15 changes: 11 additions & 4 deletions stdlib/public/runtime/SwiftDtoa.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1063,7 +1063,9 @@ size_t swift_format_float(float d, char *dest, size_t length)
int8_t digits[9];
int digitCount =
swift_decompose_float(d, digits, sizeof(digits), &decimalExponent);
if (decimalExponent < -3 || decimalExponent > 6) {
// People use float to model integers <= 2^24, so we use that
// as a cutoff for decimal vs. exponential format.
if (decimalExponent < -3 || fabsf(d) > 0x1.0p24F) {
return swift_format_exponential(dest, length, signbit(d),
digits, digitCount, decimalExponent);
} else {
Expand Down Expand Up @@ -1117,7 +1119,9 @@ size_t swift_format_double(double d, char *dest, size_t length)
int8_t digits[17];
int digitCount =
swift_decompose_double(d, digits, sizeof(digits), &decimalExponent);
if (decimalExponent < -3 || decimalExponent > 15) {
// People use double to model integers <= 2^53, so we use that
// as a cutoff for decimal vs. exponential format.
if (decimalExponent < -3 || fabs(d) > 0x1.0p53) {
return swift_format_exponential(dest, length, signbit(d),
digits, digitCount, decimalExponent);
} else {
Expand Down Expand Up @@ -1166,13 +1170,16 @@ size_t swift_format_float80(long double d, char *dest, size_t length)
}
}

// Decimal numeric formatting
// Decimal numeric formatting
int decimalExponent;
int8_t digits[21];
int digitCount =
swift_decompose_float80(d, digits, sizeof(digits), &decimalExponent);
if (decimalExponent < -3 || decimalExponent > 18) {
// People use long double to model integers <= 2^64, so we use that
// as a cutoff for decimal vs. exponential format.
// The constant is written out as a float80 (aka "long double") literal
// here since it can't be expressed as a 64-bit integer.
if (decimalExponent < -3 || fabsl(d) > 0x1.0p64L) {
return swift_format_exponential(dest, length, signbit(d),
digits, digitCount, decimalExponent);
} else {
Expand Down
48 changes: 34 additions & 14 deletions test/stdlib/PrintFloat.swift.gyb
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Original file line number Diff line number Diff line change
Expand Up @@ -544,7 +544,7 @@ PrintTests.test("Printable_Float") {
// Every power of 10 should print with only a single digit '1'
for power in -45 ... 38 {
let s: String
if power < -4 || power > 5 { // Exponential form
if power < -4 || power > 7 { // Exponential form
s = exponentialPowerOfTen(power)
} else if power < 0 { // Fractional decimal form
s = "0." + String(repeating: "0", count: -power - 1) + "1"
Expand All @@ -562,8 +562,14 @@ PrintTests.test("Printable_Float") {
expectAccurateDescription(f.nextUp)
}

// Check that the formatter chooses exponential
// format when it should:
// Float can represent all integers -(2^24)...(2^24)
let maxDecimalForm = Float(1 << 24)
expectDescription("16777216.0", maxDecimalForm)
expectDescription("-16777216.0", -maxDecimalForm)
// Outside of that range, use exponential form
expectDescription("1.6777218e+07", maxDecimalForm.nextUp)
expectDescription("-1.6777218e+07", -maxDecimalForm.nextUp)

expectDescription("1.00001", asFloat32(1.00001))
expectDescription("1.25e+17", asFloat32(125000000000000000.0))
expectDescription("1.25e+16", asFloat32(12500000000000000.0))
Expand All @@ -575,8 +581,8 @@ PrintTests.test("Printable_Float") {
expectDescription("1.25e+10", asFloat32(12500000000.0))
expectDescription("1.25e+09", asFloat32(1250000000.0))
expectDescription("1.25e+08", asFloat32(125000000.0))
expectDescription("1.25e+07", asFloat32(12500000.0))
expectDescription("1.25e+06", asFloat32(1250000.0))
expectDescription("12500000.0", asFloat32(12500000.0))
expectDescription("1250000.0", asFloat32(1250000.0))
expectDescription("125000.0", asFloat32(125000.0))
expectDescription("12500.0", asFloat32(12500.0))
expectDescription("1250.0", asFloat32(1250.0))
Expand Down Expand Up @@ -660,7 +666,7 @@ PrintTests.test("Printable_Double") {
// We know how every power of 10 should print
for power in -323 ... 308 {
let s: String
if power < -4 || power > 14 { // Exponential form
if power < -4 || power > 15 { // Exponential form
s = exponentialPowerOfTen(power)
} else if power < 0 { // Fractional decimal form
s = "0." + String(repeating: "0", count: -power - 1) + "1"
Expand All @@ -687,12 +693,18 @@ PrintTests.test("Printable_Double") {
}
}

// Check that the formatter chooses exponential
// format when it should:
// Double can represent all integers -(2^53)...(2^53)
let maxDecimalForm = Double((1 as Int64) << 53)
expectDescription("9007199254740992.0", maxDecimalForm)
expectDescription("-9007199254740992.0", -maxDecimalForm)
// Outside of that range, we use exponential form:
expectDescription("9.007199254740994e+15", maxDecimalForm.nextUp)
expectDescription("-9.007199254740994e+15", -maxDecimalForm.nextUp)

expectDescription("1.00000000000001", asFloat64(1.00000000000001))
expectDescription("1.25e+17", asFloat64(125000000000000000.0))
expectDescription("1.25e+16", asFloat64(12500000000000000.0))
expectDescription("1.25e+15", asFloat64(1250000000000000.0))
expectDescription("1250000000000000.0", asFloat64(1250000000000000.0))
expectDescription("125000000000000.0", asFloat64(125000000000000.0))
expectDescription("12500000000000.0", asFloat64(12500000000000.0))
expectDescription("1250000000000.0", asFloat64(1250000000000.0))
Expand Down Expand Up @@ -769,7 +781,7 @@ PrintTests.test("Printable_Float80") {
// We know how every power of 10 should print
for power in -4950 ... 4932 {
let s: String
if power < -4 || power > 17 { // Exponential form
if power < -4 || power > 19 { // Exponential form
s = exponentialPowerOfTen(power)
} else if power < 0 { // Fractional decimal form
s = "0." + String(repeating: "0", count: -power - 1) + "1"
Expand All @@ -794,11 +806,19 @@ PrintTests.test("Printable_Float80") {
}
}

// Check that the formatter chooses exponential
// format when it should:
// Float80 can represent all integers -(2^64)...(2^64):
let maxDecimalForm = Float80(UInt64.max) + 1.0
expectDescription("18446744073709551616.0", maxDecimalForm)
expectDescription("-18446744073709551616.0", -maxDecimalForm)
// Outside of that range, use exponential form
expectDescription("1.8446744073709551618e+19", maxDecimalForm.nextUp)
expectDescription("-1.8446744073709551618e+19", -maxDecimalForm.nextUp)

expectDescription("1.00000000000000001", asFloat80(1.00000000000000001))
expectDescription("1.25e+19", asFloat80(12500000000000000000.0))
expectDescription("1.25e+18", asFloat80(1250000000000000000.0))
expectDescription("1.25e+21", asFloat80(1250000000000000000000.0))
expectDescription("1.25e+20", asFloat80(125000000000000000000.0))
expectDescription("12500000000000000000.0", asFloat80(12500000000000000000.0))
expectDescription("1250000000000000000.0", asFloat80(1250000000000000000.0))
expectDescription("125000000000000000.0", asFloat80(125000000000000000.0))
expectDescription("12500000000000000.0", asFloat80(12500000000000000.0))
expectDescription("1250000000000000.0", asFloat80(1250000000000000.0))
Expand Down