# CVTTSS2SI — Convert With Truncation Scalar Single Precision Floating-Point Value to Integer

Opcode/Instruction | Op / En | 64/32 bit Mode Support | CPUID Feature Flag | Description
--- | --- | --- | --- | ---
F3 0F 2C /r CVTTSS2SI r32, xmm1/m32 | A | V/V | SSE | Convert one single precision floating-point value from xmm1/m32 to one signed doubleword integer in r32 using truncation.
F3 REX.W 0F 2C /r CVTTSS2SI r64, xmm1/m32 | A | V/N.E. | SSE | Convert one single precision floating-point value from xmm1/m32 to one signed quadword integer in r64 using truncation.
VEX.LIG.F3.0F.W0 2C /r 1 VCVTTSS2SI r32, xmm1/m32 | A | V/V | AVX | Convert one single precision floating-point value from xmm1/m32 to one signed doubleword integer in r32 using truncation.
VEX.LIG.F3.0F.W1 2C /r 1 VCVTTSS2SI r64, xmm1/m32 | A | V/N.E.2 | AVX | Convert one single precision floating-point value from xmm1/m32 to one signed quadword integer in r64 using truncation.
EVEX.LLIG.F3.0F.W0 2C /r VCVTTSS2SI r32, xmm1/m32{sae} | B | V/V | AVX512F | Convert one single precision floating-point value from xmm1/m32 to one signed doubleword integer in r32 using truncation.
EVEX.LLIG.F3.0F.W1 2C /r VCVTTSS2SI r64, xmm1/m32{sae} | B | V/N.E.2 | AVX512F | Convert one single precision floating-point value from xmm1/m32 to one signed quadword integer in r64 using truncation.

> 1. Software should ensure VCVTTSS2SI is encoded with VEX.L=0. Encoding VCVTTSS2SI with VEX.L=1 may encounter unpredictable behavior across different processor generations.

> 2. For this specific instruction, VEX.W/EVEX.W in non-64 bit is ignored; the instructions behaves as if the W0 version is used.

## Instruction Operand Encoding ¶

Op/En | Tuple Type | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | --- | ---
A | N/A | ModRM:reg (w) | ModRM:r/m (r) | N/A | N/A
B | Tuple1 Fixed | ModRM:reg (w) | ModRM:r/m (r) | N/A | N/A

## Description ¶

Converts a single precision floating-point value in the source operand (the second operand) to a signed doubleword integer (or signed quadword integer if operand size is 64 bits) in the destination operand (the first operand). The source operand can be an XMM register or a 32-bit memory location. The destination operand is a general purpose register. When the source operand is an XMM register, the single precision floating-point value is contained in the low doubleword of the register.

When a conversion is inexact, a truncated (round toward zero) result is returned. If a converted result is larger than the maximum signed doubleword integer, the floating-point invalid exception is raised. If this exception is masked, the indefinite integer value (80000000H or 80000000_00000000H if operand size is 64 bits) is returned.

Legacy SSE instructions: In 64-bit mode, Use of the REX.W prefix promotes the instruction to 64-bit operation. See the summary chart at the beginning of this section for encoding data and limits.

VEX.W1 and EVEX.W1 versions: promotes the instruction to produce 64-bit data in 64-bit mode.

Note: VEX.vvvv and EVEX.vvvv are reserved and must be 1111b, otherwise instructions will #UD.

Software should ensure VCVTTSS2SI is encoded with VEX.L=0. Encoding VCVTTSS2SI with VEX.L=1 may encounter unpredictable behavior across different processor generations.

## Operation ¶

### (V)CVTTSS2SI (All Versions) ¶

    IF 64-Bit Mode and OperandSize = 64
    THEN
        DEST[63:0] := Convert_Single_Precision_Floating_Point_To_Integer_Truncate(SRC[31:0]);
    ELSE
        DEST[31:0] := Convert_Single_Precision_Floating_Point_To_Integer_Truncate(SRC[31:0]);
    FI;

## Intel C/C++ Compiler Intrinsic Equivalent ¶

    VCVTTSS2SI int _mm_cvttss_i32( __m128 a);

    VCVTTSS2SI int _mm_cvtt_roundss_i32( __m128 a, int sae);

    VCVTTSS2SI __int64 _mm_cvttss_i64( __m128 a);

    VCVTTSS2SI __int64 _mm_cvtt_roundss_i64( __m128 a, int sae);

    CVTTSS2SI int _mm_cvttss_si32( __m128 a);

    CVTTSS2SI __int64 _mm_cvttss_si64( __m128 a);

## SIMD Floating-Point Exceptions ¶

Invalid, Precision.

## Other Exceptions ¶

See Table 2-20, “Type 3 Class Exception Conditions,” additionally:

#UD | If VEX.vvvv != 1111B.

EVEX-encoded instructions, see Table 2-48, “Type E3NF Class Exception Conditions.”