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stage2: fix comptime bitcast involving f80

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* Sema: implement comptime bitcast of f80 with integer-like types
  bitwise rather than taking a round trip through memory layout.
* Type: introduce `isAbiInt`.
* Value: comptime memory write of f80 writes 0 bytes for padding
  instead of leaving the memory uninitialized.
* Value: floatReadFromMemory has a more general implementation, checking
  the endianness rather than checking for specific architectures.

This fixes behavior test failures occurring on MIPS.
This commit is contained in:
Andrew Kelley
2022-07-13 13:14:37 -07:00
parent 35e7011124
commit 92bc3cbe27
4 changed files with 64 additions and 15 deletions
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10
lib/std/math/float.zig
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@@ -9,14 +9,14 @@ inline fn mantissaOne(comptime T: type) comptime_int {
/// Creates floating point type T from an unbiased exponent and raw mantissa.
inline fn reconstructFloat(comptime T: type, exponent: comptime_int, mantissa: comptime_int) T {
const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
const TBits = @Type(.{ .Int = .{ .signedness = .unsigned, .bits = @bitSizeOf(T) } });
const biased_exponent = @as(TBits, exponent + floatExponentMax(T));
return @bitCast(T, (biased_exponent << floatMantissaBits(T)) | @as(TBits, mantissa));
}
/// Returns the number of bits in the exponent of floating point type T.
pub inline fn floatExponentBits(comptime T: type) comptime_int {
assert(@typeInfo(T) == .Float);
comptime assert(@typeInfo(T) == .Float);
return switch (@typeInfo(T).Float.bits) {
16 => 5,
@@ -30,7 +30,7 @@ pub inline fn floatExponentBits(comptime T: type) comptime_int {
/// Returns the number of bits in the mantissa of floating point type T.
pub inline fn floatMantissaBits(comptime T: type) comptime_int {
assert(@typeInfo(T) == .Float);
comptime assert(@typeInfo(T) == .Float);
return switch (@typeInfo(T).Float.bits) {
16 => 10,
@@ -44,7 +44,7 @@ pub inline fn floatMantissaBits(comptime T: type) comptime_int {
/// Returns the number of fractional bits in the mantissa of floating point type T.
pub inline fn floatFractionalBits(comptime T: type) comptime_int {
assert(@typeInfo(T) == .Float);
comptime assert(@typeInfo(T) == .Float);
// standard IEEE floats have an implicit 0.m or 1.m integer part
// f80 is special and has an explicitly stored bit in the MSB
@@ -97,7 +97,7 @@ pub inline fn inf(comptime T: type) T {
return reconstructFloat(T, floatExponentMax(T) + 1, mantissaOne(T));
}
test "std.math.float" {
test "float bits" {
inline for ([_]type{ f16, f32, f64, f80, f128, c_longdouble }) |T| {
// (1 +) for the sign bit, since it is separate from the other bits
const size = 1 + floatExponentBits(T) + floatMantissaBits(T);