diff options
| -rw-r--r-- | Changelog.md | 1 | ||||
| -rw-r--r-- | docs/assembly.rst | 40 |
2 files changed, 15 insertions, 26 deletions
diff --git a/Changelog.md b/Changelog.md index b2e080a0..23de7dcd 100644 --- a/Changelog.md +++ b/Changelog.md @@ -8,6 +8,7 @@ Features: * Inline Assembly: Present proper error message when not supplying enough arguments to a functional instruction. * Inline Assembly: introduce ``keccak256`` as an opcode. ``sha3`` is still a valid alias. + * Inline Assembly: ``for`` and ``switch`` statements. Bugfixes: * Fixed crash concerning non-callable types. diff --git a/docs/assembly.rst b/docs/assembly.rst index 394fc9f5..7ef41483 100644 --- a/docs/assembly.rst +++ b/docs/assembly.rst @@ -28,11 +28,8 @@ arising when writing manual assembly by the following features: * access to external variables: ``function f(uint x) { assembly { x := sub(x, 1) } }`` * labels: ``let x := 10 repeat: x := sub(x, 1) jumpi(repeat, eq(x, 0))`` * loops: ``for { let i := 0 } lt(i, x) { i := add(i, 1) } { y := mul(2, y) }`` -* switch statements: ``switch x case 0: { y := mul(x, 2) } default: { y := 0 }`` -* function calls: ``function f(x) -> y { switch x case 0: { y := 1 } default: { y := mul(x, f(sub(x, 1))) } }`` - -.. note:: - Of the above, loops, function calls and switch statements are not yet implemented. +* switch statements: ``switch x case 0 { y := mul(x, 2) } default { y := 0 }`` +* function calls: ``function f(x) -> y { switch x case 0 { y := 1 } default { y := mul(x, f(sub(x, 1))) } }`` We now want to describe the inline assembly language in detail. @@ -501,9 +498,6 @@ is performed by replacing the variable's value on the stack by the new value. Switch ------ -.. note:: - Switch is not yet implemented. - You can use a switch statement as a very basic version of "if/else". It takes the value of an expression and compares it to several constants. The branch corresponding to the matching constant is taken. Contrary to the @@ -516,10 +510,10 @@ case called ``default``. assembly { let x := 0 switch calldataload(4) - case 0: { + case 0 { x := calldataload(0x24) } - default: { + default { x := calldataload(0x44) } sstore(0, div(x, 2)) @@ -531,13 +525,10 @@ case does require them. Loops ----- -.. note:: - Loops are not yet implemented. - Assembly supports a simple for-style loop. For-style loops have a header containing an initializing part, a condition and a post-iteration part. The condition has to be a functional-style expression, while -the other two can also be blocks. If the initializing part is a block that +the other two are blocks. If the initializing part declares any variables, the scope of these variables is extended into the body (including the condition and the post-iteration part). @@ -555,9 +546,6 @@ The following example computes the sum of an area in memory. Functions --------- -.. note:: - Functions are not yet implemented. - Assembly allows the definition of low-level functions. These take their arguments (and a return PC) from the stack and also put the results onto the stack. Calling a function looks the same way as executing a functional-style @@ -569,7 +557,7 @@ defined outside of that function. There is no explicit ``return`` statement. If you call a function that returns multiple values, you have to assign -them to a tuple using ``(a, b) := f(x)`` or ``let (a, b) := f(x)``. +them to a tuple using ``a, b := f(x)`` or ``let a, b := f(x)``. The following example implements the power function by square-and-multiply. @@ -578,12 +566,12 @@ The following example implements the power function by square-and-multiply. assembly { function power(base, exponent) -> result { switch exponent - 0: { result := 1 } - 1: { result := base } - default: { + case 0 { result := 1 } + case 1 { result := base } + default { result := power(mul(base, base), div(exponent, 2)) switch mod(exponent, 2) - 1: { result := mul(base, result) } + case 1 { result := mul(base, result) } } } } @@ -703,13 +691,13 @@ The following assembly will be generated:: mstore(0x40, 0x60) // store the "free memory pointer" // function dispatcher switch div(calldataload(0), exp(2, 226)) - case 0xb3de648b: { + case 0xb3de648b { let (r) = f(calldataload(4)) let ret := $allocate(0x20) mstore(ret, r) return(ret, 0x20) } - default: { revert(0, 0) } + default { revert(0, 0) } // memory allocator function $allocate(size) -> pos { pos := mload(0x40) @@ -860,8 +848,8 @@ Grammar:: AssemblyAssignment = '=:' Identifier LabelDefinition = Identifier ':' AssemblySwitch = 'switch' FunctionalAssemblyExpression AssemblyCase* - ( 'default' ':' AssemblyBlock )? - AssemblyCase = 'case' FunctionalAssemblyExpression ':' AssemblyBlock + ( 'default' AssemblyBlock )? + AssemblyCase = 'case' FunctionalAssemblyExpression AssemblyBlock AssemblyFunctionDefinition = 'function' Identifier '(' IdentifierList? ')' ( '->' '(' IdentifierList ')' )? AssemblyBlock AssemblyFor = 'for' ( AssemblyBlock | FunctionalAssemblyExpression) |