the defaults for the Go toolchain used to build the program,
amended to match the Go version listed in `go.mod`,
and then overridden by explicit `//go:debug` lines in the program.

The [GODEBUG History](#history) gives the exact defaults for each Go toolchain version.
For example, Go 1.21 introduces the `panicnil` setting,
controlling whether `panic(nil)` is allowed;
it defaults to `panicnil=0`, making `panic(nil)` a run-time error.

// into Go.
func testCallbackCallersSEH(t *testing.T) {
	testenv.SkipIfOptimizationOff(t) // This test requires inlining.
	if runtime.Compiler != "gc" {
		// The exact function names are not going to be the same.
		t.Skip("skipping for non-gc toolchain")
	}
	if runtime.GOARCH != "amd64" {
		// TODO: support SEH on other architectures.
		t.Skip("skipping on non-amd64")
	}

high bit is set is rejected.
</p>

<h3 id="symbols">Symbols</h3>

<p>
Some symbols, such as <code>R1</code> or <code>LR</code>,
are predefined and refer to registers.
The exact set depends on the architecture.
</p>

<p>
There are four predeclared symbols that refer to pseudo-registers.
These are not real registers, but rather virtual registers maintained by

pkg math/big, const Above Accuracy
pkg math/big, const AwayFromZero = 3
pkg math/big, const AwayFromZero RoundingMode
pkg math/big, const Below = -1
pkg math/big, const Below Accuracy
pkg math/big, const Exact = 0
pkg math/big, const Exact Accuracy
pkg math/big, const MaxExp = 2147483647
pkg math/big, const MaxExp ideal-int
pkg math/big, const MaxPrec = 4294967295
pkg math/big, const MaxPrec ideal-int

pkg debug/pe, const IMAGE_COMDAT_SELECT_ASSOCIATIVE = 5 #51868
pkg debug/pe, const IMAGE_COMDAT_SELECT_ASSOCIATIVE ideal-int #51868
pkg debug/pe, const IMAGE_COMDAT_SELECT_EXACT_MATCH = 4 #51868
pkg debug/pe, const IMAGE_COMDAT_SELECT_EXACT_MATCH ideal-int #51868
pkg debug/pe, const IMAGE_COMDAT_SELECT_LARGEST = 6 #51868
pkg debug/pe, const IMAGE_COMDAT_SELECT_LARGEST ideal-int #51868

		{data2[:511], 0, io.ErrUnexpectedEOF},
		{data2[:512], 1, io.ErrUnexpectedEOF},
		{data2[:1195], 1, io.ErrUnexpectedEOF},
		{data2[:1196], 1, io.EOF}, // Exact end of data and start of padding
		{data2[:1200], 1, io.EOF},
		{data2[:1535], 1, io.EOF},
		{data2[:1536], 1, io.EOF}, // Exact end of padding
		{data2[:1536] + trash[:1], 1, io.ErrUnexpectedEOF},
		{data2[:1536] + trash[:511], 1, io.ErrUnexpectedEOF},

		}
		w.emitf("const %s %s", obj.Name(), w.typeString(obj.Type()))
		x := obj.Val()
		short := x.String()
		exact := x.ExactString()
		if short == exact {
			w.emitf("const %s = %s", obj.Name(), short)
		} else {
			w.emitf("const %s = %s  // %s", obj.Name(), short, exact)
		}
	case *types.Var:
		if w.isDeprecated(obj) {
			w.emitf("var %s //deprecated", obj.Name())
		}

			}
		}
	})
}

// Test that the stack can be unwound through a call out and call back
// into Go.
func testCallbackCallers(t *testing.T) {
	if runtime.Compiler != "gc" {
		// The exact function names are not going to be the same.
		t.Skip("skipping for non-gc toolchain")
	}
	pc := make([]uintptr, 100)
	n := 0
	name := []string{
		"runtime.cgocallbackg1",
		"runtime.cgocallbackg",

</p>

<p>
In general, complex constants are a form of
<a href="#Constant_expressions">constant expression</a>
and are discussed in that section.
</p>

<p>
Numeric constants represent exact values of arbitrary precision and do not overflow.
Consequently, there are no constants denoting the IEEE 754 negative zero, infinity,
and not-a-number values.
</p>

<p>

// characters, as defined by unicode.IsSpace, returning a slice of subslices of s or an
// empty slice if s contains only white space.
func Fields(s []byte) [][]byte {
	// First count the fields.
	// This is an exact count if s is ASCII, otherwise it is an approximation.
	n := 0
	wasSpace := 1
	// setBits is used to track which bits are set in the bytes of s.
	setBits := uint8(0)
	for i := 0; i < len(s); i++ {
		r := s[i]