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Fixed IMUL_RCP if divisor is a power of 2

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tevador
2019-05-04 18:00:17 +02:00
parent 197cd90e07
commit b1f1e1d6ad
5 changed files with 14 additions and 10 deletions
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doc/specs.md
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@@ -519,7 +519,7 @@ This instructions adds the values of two registers (modulo 2<sup>64</sup>). The
These instructions output the high 64 bits of the whole 128-bit multiplication result. The result differs for signed and unsigned multiplication (IMULH is unsigned, ISMULH is signed). The variants with a register source operand perform a squaring operation if `dst` equals `src`.
#### 5.2.6 IMUL_RCP
This instruction multiplies the destination register by a reciprocal of `imm32` (the immediate value is zero-extended and treated as unsigned). The reciprocal is calculated as <code>rcp = 2<sup>x</sup> / imm32</code> by choosing the largest integer `x` such that <code>rcp < 2<sup>64</sup></code>. If `imm32` equals 0, IMUL_RCP is a no-op.
If `imm32` equals 0 or is a power of 2, IMUL_RCP is a no-op. In other cases, the instruction multiplies the destination register by a reciprocal of `imm32` (the immediate value is zero-extended and treated as unsigned). The reciprocal is calculated as <code>rcp = 2<sup>x</sup> / imm32</code> by choosing the largest integer `x` such that <code>rcp < 2<sup>64</sup></code>.
#### 5.2.7 INEG_R
Performs two's complement negation of the destination register.
@@ -607,7 +607,7 @@ This instruction performs a conditional jump in the Program Buffer. It uses an i
A register is considered as modified by an instruction in the following cases:
* It is the destination register of an integer instruction except IMUL_RCP and ISWAP_R.
* It is the destination register of IMUL_RCP and `imm32` is not zero.
* It is the destination register of IMUL_RCP and `imm32` is not zero or a power of 2.
* It is the source or the destination register of ISWAP_R and the destination and source registers are distinct.
* The CBRANCH instruction is considered to modify all integer registers.