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spec: document signed integer shift counts 

Updates #19113.

Change-Id: I4726f51c5061c33979cdd061f6d4616fa97edb9a
Reviewed-on: https://go-review.googlesource.com/c/161201
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Robert Griesemer 2019-02-05 14:33:24 -08:00
parent 5aac0f0d1e
commit a10b4cff91
1 changed files with 6 additions and 4 deletions
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10
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{ <!--{
"Title": "The Go Programming Language Specification", "Title": "The Go Programming Language Specification",
"Subtitle": "Version of November 16, 2018", "Subtitle": "Version of February 16, 2019",
"Path": "/ref/spec" "Path": "/ref/spec"
}--> }-->
@ -3439,7 +3439,7 @@ to the type of the other operand.
</p> </p>
<p> <p>
The right operand in a shift expression must have unsigned integer type The right operand in a shift expression must have integer type
or be an untyped constant <a href="#Representability">representable</a> by a or be an untyped constant <a href="#Representability">representable</a> by a
value of type <code>uint</code>. value of type <code>uint</code>.
If the left operand of a non-constant shift expression is an untyped constant, If the left operand of a non-constant shift expression is an untyped constant,
@ -3586,7 +3586,9 @@ be replaced by a bitwise AND operation:
<p> <p>
The shift operators shift the left operand by the shift count specified by the The shift operators shift the left operand by the shift count specified by the
right operand. They implement arithmetic shifts if the left operand is a signed right operand, which must be positive. If the shift count is negative at run time,
a <a href="#Run_time_panics">run-time panic</a> occurs.
The shift operators implement arithmetic shifts if the left operand is a signed
integer and logical shifts if it is an unsigned integer. integer and logical shifts if it is an unsigned integer.
There is no upper limit on the shift count. Shifts behave There is no upper limit on the shift count. Shifts behave
as if the left operand is shifted <code>n</code> times by 1 for a shift as if the left operand is shifted <code>n</code> times by 1 for a shift
@ -5921,7 +5923,7 @@ var a = complex(2, -2) // complex128
const b = complex(1.0, -1.4) // untyped complex constant 1 - 1.4i const b = complex(1.0, -1.4) // untyped complex constant 1 - 1.4i
x := float32(math.Cos(math.Pi/2)) // float32 x := float32(math.Cos(math.Pi/2)) // float32
var c64 = complex(5, -x) // complex64 var c64 = complex(5, -x) // complex64
var s uint = complex(1, 0) // untyped complex constant 1 + 0i can be converted to uint var s int = complex(1, 0) // untyped complex constant 1 + 0i can be converted to int
_ = complex(1, 2&lt;&lt;s) // illegal: 2 assumes floating-point type, cannot shift _ = complex(1, 2&lt;&lt;s) // illegal: 2 assumes floating-point type, cannot shift
var rl = real(c64) // float32 var rl = real(c64) // float32
var im = imag(a) // float64 var im = imag(a) // float64